Create opensocial-data-base 'feature', and use this when rewriter succeeds

This patch:
- Extracts opensocial-data-base as a private 'feature' from opensocial-data
- Rewrites that JS a bit to hide internal state and APIs where possible
- Adds generic functionality for a rewriter to add or remove features from a gadget as MutableContent methods
- Changes the PipelineDataContentRewriter to swap out opensocial-data and swap in opensocial-data-base when all pipelines successfully resolve

[awiner, 2009-02-21 00:29:43]

Tests to come before submitting, but this patch makes MutableContent still
uglier, so if anyone has good ideas for cleaning that up, it'd be appreciated.

[louiscryan, 2009-02-21 01:37:45]

The MutableContent change probably makes more sense on o.a.s.gadgets.Gadget.
Everything else looks good

http://codereview.appspot.com/20043/diff/1/4
File
java/gadgets/src/main/java/org/apache/shindig/gadgets/rewrite/MutableContent.java
(right):

http://codereview.appspot.com/20043/diff/1/4#newcode165
Line 165: public void addFeature(String name) {
Gadget is probably a better home for this

http://codereview.appspot.com/20043/diff/1/4#newcode183
Line 183: return ImmutableSet.<String>of();
Collections.emptySet ?

[levik, 2009-02-21 16:00:55]

http://codereview.appspot.com/20043/diff/1/5
File features/features.txt (right):

http://codereview.appspot.com/20043/diff/1/5#newcode19
Line 19: features/opensocial-data-base/feature.xml
would "data-store" be a better name? -base conjures up images of SQL :)

[awiner, 2009-02-23 23:37:19]

http://codereview.appspot.com/20043/diff/1/5
File features/features.txt (right):

http://codereview.appspot.com/20043/diff/1/5#newcode19
Line 19: features/opensocial-data-base/feature.xml
On 2009/02/21 16:00:55, levik wrote:
> would "data-store" be a better name? -base conjures up images of SQL :)

Changed to opensocial-data-context

http://codereview.appspot.com/20043/diff/1/4
File
java/gadgets/src/main/java/org/apache/shindig/gadgets/rewrite/MutableContent.java
(right):

http://codereview.appspot.com/20043/diff/1/4#newcode165
Line 165: public void addFeature(String name) {
On 2009/02/21 01:37:45, louiscryan wrote:
> Gadget is probably a better home for this

Done.

http://codereview.appspot.com/20043/diff/1/4#newcode183
Line 183: return ImmutableSet.<String>of();
On 2009/02/21 01:37:45, louiscryan wrote:
> Collections.emptySet ?

They're (in essence) the same thing - a shared singleton.  I use ImmutableXyz a
fair bit, so this is more consistent for me.  OTOH, Shindig tends to use
Collections.emptySet(), so that's probably better.