Convert makeRequest code paths to use JsonSerializer instead of direct JSONObject calls

[etnu00]

Reviewers: shindig.remailer,

Message:
Attempting to clean up remaining JSONObject usage for performance and
security.


Please review this at http://codereview.appspot.com/33061

Affected files:
  M     java/common/src/test/java/org/apache/shindig/common/JsonAssert.java
  M      
java/gadgets/src/main/java/org/apache/shindig/gadgets/FetchResponseUtils.java
  M      
java/gadgets/src/main/java/org/apache/shindig/gadgets/preload/HttpPreloader.java
  M      
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/MakeRequestHandler.java
  M      
java/gadgets/src/test/java/org/apache/shindig/gadgets/FetchResponseUtilsTest.java
  M      
java/gadgets/src/test/java/org/apache/shindig/gadgets/preload/HttpPreloaderTest.java