normalise header name to lowecase

browser/lib/transport/xhrrequest.js

@@ -48,7 +48,7 @@ var XHRRequest = (function() {
 			headers = {};
 		for (var i = 0; i < headerPairs.length; i++) {
 			var parts = Utils.arrMap(headerPairs[i].split(':'), Utils.trim);
-			headers[parts[0]] = parts[1];
+			headers[parts[0].toLowerCase()] = parts[1];
 		}
 		return headers;
 	}