fixes #722 - throw step errors are no more silenced

Introduced a new Casper `silentErrors` option which is set to `false`
by default.

@@ -281,6 +281,17 @@ When this option is set to true — which is the default, any password informat
 
 .. index:: Step stack, timeout
 
+``silentErrors``
+-------------------------------------------------------------------------------
+
+**Type:** ``Boolean``
+
+**Default:** ``false``
+
+When this option is enabled, caught step errors are not thrown (though related events are still emitted). Mostly used internally in a testing context.
+
+.. index:: timeout
+
 ``stepTimeout``
 -------------------------------------------------------------------------------
 

@@ -116,6 +116,7 @@ var Casper = function Casper(options) {
             userAgent:                     defaultUserAgent
         },
         remoteScripts:       [],
+        silentErrors:        false,
         stepTimeout:         null,
         timeout:             null,
         verbose:             false,
@@ -384,6 +385,9 @@ Casper.prototype.checkStep = function checkStep(self, onComplete) {
         }
     } catch (error) {
         self.emit('complete.error', error);
+        if (!self.options.silentErrors) {
+            throw error;
+        }
     }
 };
 
@@ -1528,6 +1532,9 @@ Casper.prototype.runStep = function runStep(step) {
         }
     } catch (err) {
         this.emit('step.error', err);
+        if (!this.options.silentErrors) {
+            throw err;
+        }
     }
     if (!skipLog) {
         this.emit('step.complete', stepResult);
@@ -1981,6 +1988,9 @@ Casper.prototype.wait = function wait(timeout, then) {
                     then.call(self, self);
                 } catch (error) {
                     self.emit('wait.error', error);
+                    if (!self.options.silentErrors) {
+                        throw error;
+                    }
                 }
             }
             self.waitDone();
@@ -2044,6 +2054,9 @@ Casper.prototype.waitFor = function waitFor(testFx, then, onTimeout, timeout, de
                     return onWaitTimeout.call(self, timeout, details);
                 } catch (error) {
                     self.emit('waitFor.timeout.error', error);
+                    if (!self.options.silentErrors) {
+                        throw error;
+                    }
                 } finally {
                     return;
                 }

@@ -13,7 +13,8 @@ var f            = utils.format;
 var loadIncludes = ['includes', 'pre', 'post'];
 var tests        = [];
 var casper       = require('casper').create({
-    exitOnError: false
+    exitOnError: false,
+    silentErrors: true // we subscribe to error events for catching them
 });
 
 // local utils