Kill ResponseError

[awiner]

Reviewers: shindig.remailer_gmail.com,

Message:
This is what it looks like to kill off ResponseError, and just go with
HTTP error codes.  I've kept the JSON-RPC message code consistent,
though that could go too.


Please review this at http://codereview.appspot.com/45044

Affected files:
  M      
java/common/src/main/java/org/apache/shindig/protocol/ApiServlet.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/BaseRequestItem.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/DataServiceServlet.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/DefaultHandlerRegistry.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/HandlerPreconditions.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/JsonRpcServlet.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/ProtocolException.java
  D      
java/common/src/main/java/org/apache/shindig/protocol/ResponseError.java
  M      
java/common/src/main/java/org/apache/shindig/protocol/ResponseItem.java
  M      
java/common/src/test/java/org/apache/shindig/protocol/DataServiceServletTest.java
  M      
java/common/src/test/java/org/apache/shindig/protocol/DefaultHandlerRegistryTest.java
  M      
java/common/src/test/java/org/apache/shindig/protocol/TestHandler.java
  M      
java/gadgets/src/main/java/org/apache/shindig/gadgets/http/InvalidationHandler.java
  M      
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/HttpRequestHandler.java
  M      
java/social-api/src/main/java/org/apache/shindig/social/opensocial/service/AppDataHandler.java
  M      
java/social-api/src/main/java/org/apache/shindig/social/opensocial/service/MessageHandler.java
  M      
java/social-api/src/main/java/org/apache/shindig/social/opensocial/spi/SocialSpiException.java
  M      
java/social-api/src/main/java/org/apache/shindig/social/sample/service/SampleContainerHandler.java
  M      
java/social-api/src/main/java/org/apache/shindig/social/sample/spi/JsonDbOpensocialService.java
  M      
java/social-api/src/test/java/org/apache/shindig/social/opensocial/service/AppDataHandlerTest.java
  M      
java/social-api/src/test/java/org/apache/shindig/social/opensocial/service/ResponseItemTest.java
  M      
java/social-api/src/test/java/org/apache/shindig/social/sample/spi/JsonDbOpensocialServiceTest.java