Add test to verify glTexSubImage2D() with depth formats

This test verifies the bug fix in i965 drivers in mesa commit 984a02b.
Reproduces another bug in the driver with GL_DEPTH_COMPONENT16
internal format.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
glsl-1.10/fragdepth: add new, simple test of gl_FragDepth