With this patch we can bind pbuffers as textures. Once we add support for using
a sharing handle to create a pbuffer we can use this to allow us to use it as a
texture as well.

BUG=129
TEST=modified Simple_Texture2D works
Review URL: http://codereview.appspot.com/4291066/

git-svn-id: https://angleproject.googlecode.com/svn/trunk@604 736b8ea6-26fd-11df-bfd4-992fa37f6226