Make it possible to force the Ajax crossDomain option to false.

src/ajax.js

@@ -310,6 +310,7 @@ jQuery.extend({
 		contentType: "application/x-www-form-urlencoded",
 		processData: true,
 		async: true,
+		crossDomain: null,
 		/*
 		timeout: 0,
 		data: null,
@@ -319,7 +320,6 @@ jQuery.extend({
 		cache: null,
 		traditional: false,
 		headers: {},
-		crossDomain: null,
 		*/
 
 		accepts: {
@@ -604,7 +604,7 @@ jQuery.extend({
 		s.dataTypes = jQuery.trim( s.dataType || "*" ).toLowerCase().split( rspacesAjax );
 
 		// Determine if a cross-domain request is in order
-		if ( !s.crossDomain ) {
+		if ( s.crossDomain == null ) {
 			parts = rurl.exec( s.url.toLowerCase() );
 			s.crossDomain = !!( parts &&
 				( parts[ 1 ] != ajaxLocParts[ 1 ] || parts[ 2 ] != ajaxLocParts[ 2 ] ||