Also addded the checks for framebuffer completeness as defined by the ES2 spec and EXT_draw_buffers.

TRAC #22656

Signed-off-by: Nicolas Capens
Signed-off-by: Shannon Woods
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2065 736b8ea6-26fd-11df-bfd4-992fa37f6226