Fix compressed texture loads for non-minimal pitches

Fix compressed texture loads for non-minimal pitches

The current glCompressedTexImage support in the state tracker assumes
that compressed textures have minimal pitch.

However, in some cases this is not true, such as for mipmaps of non-POT
compressed textures on nVidia hardware.

This patch adds a check and does a memcpy for each line instead of the
whole image in that case.

Signed-off-by: Keith Whitwell <keithw@vmware.com>
Tweaks for C90 compilation.