Per-browser rpc.js

[jo...@gmail.com]

Reviewers: shindig.remailer_gmail.com,

Description:
Implementation of JsFeatureLoader that loads only the rpc.js transport
code needed by the target browser.

To use this, a concrete implementation of UserAgent.Parser must be
provided and bound. In addition, JsFeatureLoader must be bound to
implementation SmartRpcJsFeatureLoader.

This code is not widely tested, and should be deemed experimental.

Please review this at http://codereview.appspot.com/63210

Affected files:
    
java/common/src/main/java/org/apache/shindig/common/servlet/HttpServletUserAgentProvider.java
   java/common/src/main/java/org/apache/shindig/common/servlet/UserAgent.java
    
java/common/src/test/java/org/apache/shindig/common/servlet/HttpServletUserAgentProviderTest.java
    
java/common/src/test/java/org/apache/shindig/common/servlet/UserAgentTest.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/SmartRpcJsFeatureLoader.java
    
java/gadgets/src/test/java/org/apache/shindig/gadgets/JsFeatureLoaderTest.java
    
java/gadgets/src/test/java/org/apache/shindig/gadgets/SmartRpcJsFeatureLoaderTest.java