TRAC #12496

Derive Renderbuffer, Texture and Buffer from RefCountObject.
This class keeps a reference count for all objects that need cross-context
reference counting, and also the object id.
Restructure Renderbuffers to create a wrapper object and a storage object.
Use BindingPointer for all binding points instead of binding by object id.

Signed-off-by: Shannon Woods
Signed-off-by: Daniel Koch

git-svn-id: https://angleproject.googlecode.com/svn/trunk@364 736b8ea6-26fd-11df-bfd4-992fa37f6226