Support for multipart/form-data @ JsonRpcServlet

[therealsachin]

Reviewers: awiner, louiscryan,

Description:
As per the RPC Spec for content upload, shindig needs to support
multipart/form-data handling. This does the required changes to support
it.
Please review this at http://codereview.appspot.com/21068

Affected files:
  java/common/pom.xml
  java/common/src/main/java/org/apache/shindig/protocol/BaseRequestItem.java
   
java/common/src/main/java/org/apache/shindig/protocol/DefaultHandlerRegistry.java
  java/common/src/main/java/org/apache/shindig/protocol/JsonRpcServlet.java
  java/common/src/main/java/org/apache/shindig/protocol/RequestItem.java
  java/common/src/main/java/org/apache/shindig/protocol/RpcHandler.java
   
java/common/src/main/java/org/apache/shindig/protocol/multipart/CommonsFormDataItem.java
   
java/common/src/main/java/org/apache/shindig/protocol/multipart/DefaultMultipartFormParser.java
   
java/common/src/main/java/org/apache/shindig/protocol/multipart/FormDataItem.java
   
java/common/src/main/java/org/apache/shindig/protocol/multipart/MultipartFormParser.java
   
java/common/src/test/java/org/apache/shindig/protocol/BaseRequestItemTest.java
   
java/common/src/test/java/org/apache/shindig/protocol/DefaultHandlerRegistryTest.java
   
java/common/src/test/java/org/apache/shindig/protocol/JsonRpcServletTest.java
   
java/common/src/test/java/org/apache/shindig/protocol/multipart/DefaultMultipartFormParserTest.java
   
java/social-api/src/main/java/org/apache/shindig/social/opensocial/service/SocialRequestItem.java
  pom.xml