Fix 11547. XML and IE DOM can't be force-lowercase in removeAttr().

See discussion on pull request: https://github.com/jquery/jquery/pull/724

src/attributes.js

@@ -356,7 +356,12 @@ jQuery.extend({
 			i = 0;
 
 		if ( value && elem.nodeType === 1 ) {
-			attrNames = value.toLowerCase().split( rspace );
+
+			if ( !jQuery.isXMLDoc( elem ) ) {
+				value = value.toLowerCase();
+			}
+
+			attrNames = value.split( rspace );
 			l = attrNames.length;
 
 			for ( ; i < l; i++ ) {

test/unit/attributes.js

@@ -1192,3 +1192,16 @@ test("coords returns correct values in IE6/IE7, see #10828", function() {
 	area = map.html("<area shape='rect' href='#' alt='a' /></map>").find("area");
 	equal( area.attr("coords"), undefined, "did not retrieve coords correctly");
 });
+
+test("Handle cased attributes on XML DOM correctly in removeAttr()", function() {
+	expect(1);
+
+	var xmlStr = "<root><item fooBar='123' /></root>",
+		$xmlDoc = jQuery( jQuery.parseXML( xmlStr ) ),
+		$item = $xmlDoc.find( "item" ),
+		el = $item[0];
+
+	$item.removeAttr( "fooBar" );
+
+	equal( el.attributes.length, 0, "attribute with upper case did not get removed" );
+});