Added `reset` option to Casper#sendKeys()

This will empty current field value before sending keys to it.

@@ -1466,8 +1466,11 @@ The currently supported HTMLElements that can receive keyboard events from ``sen
 Options
 ~~~~~~~
 
-- ``(Boolean) keepFocus``:
+- ``(Boolean) reset``:
+
+  When set to ``true``, this option will first empty the current field value. By default, it's set to ``false`` and ``sendKeys()`` will just append string to the current field value.
 
+- ``(Boolean) keepFocus``:
 
   ``sendKeys()`` by default will remove the focus on text input fields, which   will typically close autocomplete widgets. If you want to maintain focus, use   the ``keepFocus`` option. For example, if using jQuery-UI, you can click on   the first autocomplete suggestion using::
 

@@ -1555,7 +1555,8 @@ Casper.prototype.sendKeys = function(selector, keys, options) {
     "use strict";
     this.checkStarted();
     options = utils.mergeObjects({
-        eventType: 'keypress'
+        eventType: 'keypress',
+        reset: false
     }, options || {});
     var elemInfos = this.getElementInfo(selector),
         tag = elemInfos.nodeName.toLowerCase(),
@@ -1573,6 +1574,12 @@ Casper.prototype.sendKeys = function(selector, keys, options) {
         isTextInput = true;
         this.click(selector);
     }
+    if (options.reset) {
+        this.evaluate(function(selector) {
+            __utils__.setField(__utils__.findOne(selector), '');
+        }, selector);
+        this.click(selector);
+    }
     var modifiers = utils.computeModifier(options && options.modifiers,
                                           this.page.event.modifier)
     this.page.sendEvent(options.eventType, keys, null, null, modifiers);

@@ -26,7 +26,7 @@
         </form>
         <form id="no-type-test-form" action="#" enctype="multipart/form-data">
             <input name="notype">
-        <form>
+        </form>
 
         <script>
             (function () {

@@ -59,3 +59,14 @@ if (utils.gteVersion(phantom.version, '1.9.0')) {
         });
     });
 }
+
+casper.test.begin('sendKeys() reset option', 1, function(test) {
+    casper.start('tests/site/form.html', function() {
+        this.sendKeys('textarea', 'foo');
+        this.sendKeys('textarea', 'bar', {reset: true});
+        var values = this.getFormValues('form[action="result.html"]');
+        test.assertEquals(values.content, "bar");
+    }).run(function() {
+        test.done();
+    });
+});