updated the way exceptions are thrown; now using throw new Error() everywhere

@@ -208,7 +208,7 @@
                     try {
                         onComplete.call(self, self);
                     } catch (err) {
-                        self.log("could not complete final step: " + err, "error");
+                        self.log("Could not complete final step: " + err, "error");
                     }
                 } else {
                     // default behavior is to exit phantom
@@ -245,7 +245,7 @@
          */
         createStep: function(fn, options) {
             if (!isType(fn, "function")) {
-                throw "createStep(): a step definition must be a function";
+                throw new Error("createStep(): a step definition must be a function");
             }
             fn.options = isType(options, "object") ? options : {};
             return fn;
@@ -447,10 +447,10 @@
         fill: function(selector, vals, submit) {
             submit = submit === true ? submit : false;
             if (!isType(selector, "string") || !selector.length) {
-                throw "form selector must be a non-empty string";
+                throw new Error("Form selector must be a non-empty string");
             }
             if (!isType(vals, "object")) {
-                throw "form values must be provided as an object";
+                throw new Error("Form values must be provided as an object");
             }
             var fillResults = this.evaluate(function(selector, values) {
                return __utils__.fill(selector, values);
@@ -459,7 +459,7 @@
                 values:   vals
             });
             if (!fillResults) {
-                throw "unable to fill form";
+                throw new Error("Unable to fill form");
             } else if (fillResults.errors.length > 0) {
                 (function(self){
                     fillResults.errors.forEach(function(error) {
@@ -467,7 +467,7 @@
                     });
                 })(this);
                 if (submit) {
-                    this.log("errors encountered while filling form; submission aborted", "warning");
+                    this.log("Errors encountered while filling form; submission aborted", "warning");
                     submit = false;
                 }
             }
@@ -708,10 +708,10 @@
          */
         setHttpAuth: function(username, password) {
             if (!this.started) {
-                throw "Casper must be started in order to use the setHttpAuth() method";
+                throw new Error("Casper must be started in order to use the setHttpAuth() method");
             }
             if (!isType(username, "string") || !isType(password, "string")) {
-                throw "Both username and password must be strings";
+                throw new Error("Both username and password must be strings");
             }
             this.page.settings.userName = username;
             this.page.settings.password = password;
@@ -783,10 +783,10 @@
          */
         then: function(step) {
             if (!this.started) {
-                throw "Casper not started; please use Casper#start";
+                throw new Error("Casper not started; please use Casper#start");
             }
             if (!isType(step, "function")) {
-                throw "You can only define a step as a function";
+                throw new Error("You can only define a step as a function");
             }
             // check if casper is running
             if (this.checker === null) {
@@ -1066,7 +1066,7 @@
      */
     phantom.Casper.extend = function(proto) {
         if (!isType(proto, "object")) {
-            throw "extends() only accept objects as prototypes";
+            throw new Error("extends() only accept objects as prototypes");
         }
         mergeObjects(phantom.Casper.prototype, proto);
     };

@@ -32,7 +32,7 @@
      */
     phantom.Casper.FunctionArgsInjector = function(fn) {
         if (!isType(fn, "function")) {
-            throw "FunctionArgsInjector() can only process functions";
+            throw new Error("FunctionArgsInjector() can only process functions");
         }
         this.fn = fn;
 
@@ -55,7 +55,7 @@
         this.process = function(values) {
             var fnObj = this.extract(this.fn);
             if (!isType(fnObj, "object")) {
-                throw "Unable to process function " + this.fn.toString();
+                throw new Error("Unable to process function " + this.fn.toString());
             }
             var inject = this.getArgsInjectionString(fnObj.args, values);
             return 'function ' + (fnObj.name || '') + '(){' + inject + fnObj.body + '}';

@@ -38,7 +38,7 @@
         this.options = isType(options, "object") ? options : {};
 
         if (!casper instanceof phantom.Casper) {
-            throw "phantom.Casper.Tester needs a phantom.Casper instance";
+            throw new Error("phantom.Casper.Tester needs a phantom.Casper instance");
         }
 
         // locals
@@ -276,7 +276,7 @@
          */
         this.exec = function(file) {
             if (!fs.isFile(file) || !isJsFile(file)) {
-                throw "Can only exec() files with .js or .coffee extensions";
+                throw new Error("Can only exec() files with .js or .coffee extensions");
             }
             if (fileExt(file) === "coffee") {
                 phantom.injectJs(file); // FIXME: syntax validation?
@@ -286,7 +286,7 @@
                 try {
                     parsed = esprima.parse(testContents);
                 } catch(e) {
-                    throw "Unable to parse test file " + file + ": " + e.toString();
+                    throw new Error("Unable to parse test file " + file + ": " + e.toString());
                 }
                 eval(testContents);
             }
@@ -395,7 +395,7 @@
         this.runSuites = function() {
             var testFiles = [], self = this;
             if (arguments.length === 0) {
-                throw "No test suite to run";
+                throw new Error("No test suite to run");
             }
             Array.prototype.forEach.call(arguments, function(path) {
                 if (!fs.exists(path)) {