Implements a special case for temporary surface creation for DXT low mip levels. TRAC #12908 The lowest mip levels for DXT textures will have dimensions < 4, so a D3D texture cannot be created to hold them offscreen directly. Instead, we must create a larger texture one of whose mip levels would be the desired dimension, and store the surface from that texture for later inclusion in the final texture. Signed-off-by: Daniel Koch Author: Shannon Woods git-svn-id: https://angleproject.googlecode.com/svn/trunk@398 736b8ea6-26fd-11df-bfd4-992fa37f6226