Optimized the clean() code to no longer use .trim() (speeds up working against...

Optimized the clean() code to no longer use .trim() (speeds up working against long HTML in IE). Fixes #4037.

src/core.js

@@ -855,7 +855,7 @@ jQuery.extend({
 				});
 
 				// Trim whitespace, otherwise indexOf won't work as expected
-				var tags = jQuery.trim( elem ).toLowerCase();
+				var tags = elem.replace(/^\s+/, "").substring(0, 10).toLowerCase();
 
 				var wrap =
 					// option or optgroup
@@ -895,11 +895,12 @@ jQuery.extend({
 				if ( !jQuery.support.tbody ) {
 
 					// String was a <table>, *may* have spurious <tbody>
-					var tbody = !tags.indexOf("<table") && tags.indexOf("<tbody") < 0 ?
-						div.firstChild && div.firstChild.childNodes :
+					var hasBody = /<tbody/i.test(elem),
+						tbody = !tags.indexOf("<table") && !hasBody ?
+							div.firstChild && div.firstChild.childNodes :
 
 						// String was a bare <thead> or <tfoot>
-						wrap[1] == "<table>" && tags.indexOf("<tbody") < 0 ?
+						wrap[1] == "<table>" && !hasBody ?
 							div.childNodes :
 							[];