Ensured that the mUsesPointSprites flag is properly preserved when loading shaders from binary cache.

BUG=https://code.google.com/p/angleproject/issues/detail?id=389
Review URL: https://codereview.appspot.com/6884053

git-svn-id: https://angleproject.googlecode.com/svn/trunk@1560 736b8ea6-26fd-11df-bfd4-992fa37f6226