IE doesn't like doing attaching the mergeNum property to XML documents, so for...

IE doesn't like doing attaching the mergeNum property to XML documents, so for now, we're just going to (possibly) return duplicates in IE, in XML documents. (bug #1357).

src/jquery/jquery.js

@@ -1666,11 +1666,15 @@ jQuery.extend({
 	unique: function(first) {
 		var r = [], num = jQuery.mergeNum++;
 
+		try {
 			for ( var i = 0, fl = first.length; i < fl; i++ )
 				if ( num != first[i].mergeNum ) {
 					first[i].mergeNum = num;
 					r.push(first[i]);
 				}
+		} catch(e) {
+			r = first;
+		}
 
 		return r;
 	},