fix($http): ignore xhr.responseType setter exception if value is "json"

src/ng/httpBackend.js

@@ -107,7 +107,20 @@ function createHttpBackend($browser, createXhr, $browserDefer, callbacks, rawDoc
       }
 
       if (responseType) {
-        xhr.responseType = responseType;
+        try {
+          xhr.responseType = responseType;
+        } catch (e) {
+          // WebKit added support for the json responseType value on 09/03/2013
+          // https://bugs.webkit.org/show_bug.cgi?id=73648. Versions of Safari prior to 7 are
+          // known to throw when setting the value "json" as the response type. Other older
+          // browsers implementing the responseType 
+          //
+          // The json response type can be ignored if not supported, because JSON payloads are
+          // parsed on the client-side regardless.
+          if (responseType !== 'json') {
+            throw e;
+          }
+        }
       }
 
       xhr.send(post || null);