jQuery.ajax: Document contentType false

Added Boolean as a type for contentType.
Added a sentance about what passing false does for contentType

Ref gh-547
Ref gh-369

Author: gnarf

entries/jQuery.ajax.xml

@@ -37,8 +37,10 @@
       <property name="contents" type="PlainObject" added="1.5">
         <desc>An object of string/regular-expression pairs that determine how jQuery will parse the response, given its content type.</desc>
       </property>
-      <property default="'application/x-www-form-urlencoded; charset=UTF-8'" name="contentType" type="String">
-        <desc>When sending data to the server, use this content type. Default is "application/x-www-form-urlencoded; charset=UTF-8", which is fine for most cases. If you explicitly pass in a content-type to <code>$.ajax()</code>, then it is always sent to the server (even if no data is sent). The W3C XMLHttpRequest specification dictates that the charset is always UTF-8; specifying another charset will not force the browser to change the encoding. <strong>Note:</strong> For cross-domain requests, setting the content type to anything other than <code>application/x-www-form-urlencoded</code>, <code>multipart/form-data</code>, or <code>text/plain</code> will trigger the browser to send a preflight OPTIONS request to the server.</desc>
+      <property default="'application/x-www-form-urlencoded; charset=UTF-8'" name="contentType">
+        <type name="Boolean"/>
+        <type name="String"/>
+        <desc>When sending data to the server, use this content type. Default is "application/x-www-form-urlencoded; charset=UTF-8", which is fine for most cases.  If you explicitly pass in a content-type to <code>$.ajax()</code>, then it is always sent to the server (even if no data is sent).  As of jQuery 1.6 you can pass <code>false</code> to tell jQuery to not set any content type header.  <strong>Note:</strong> The W3C XMLHttpRequest specification dictates that the charset is always UTF-8; specifying another charset will not force the browser to change the encoding. <strong>Note:</strong> For cross-domain requests, setting the content type to anything other than <code>application/x-www-form-urlencoded</code>, <code>multipart/form-data</code>, or <code>text/plain</code> will trigger the browser to send a preflight OPTIONS request to the server.</desc>
       </property>
       <property name="context" type="PlainObject">
         <desc>This object will be made the context of all Ajax-related callbacks. By default, the context is an object that represents the ajax settings used in the call (<code>$.ajaxSettings</code> merged with the settings passed to <code>$.ajax</code>). For example,  specifying a DOM element as the context will make that the context for the <code>complete</code> callback of a request, like so: