mesa: add texobj support for ARB_texture_multisample

mesa: add texobj support for ARB_texture_multisample

Adds the new texture targets, and per-image state for GL_TEXTURE_SAMPLES
and GL_TEXTURE_FIXED_SAMPLE_LOCATIONS.

V2: - Allow multisample texture targets in glInvalidateTexSubImage too.
      This was already partly there, but I missed it the first time around
      since the interaction is defined in a newer extension. Fixed weird
      indentation.
    - Allow multisample array textures in glFramebufferTextureLayer.
      This was overlooked as the tests originally only used 2d
      multisample textures.

V3: - Set min/mag filters sensibly for multisample textures. This
      can't actually be changed by the user, so it's more sensible to
      initialize it correctly than to hack around it being bogus later.

V4: - Tidy up initial min/mag filter setup. Setup in
      _mesa_initialize_texture_object was bogus, but benign since
      finish_texture_init() clobbered everything with correct values. For V4,
      just do the setup in finish_texture_init().

V5: - Don't break glPopAttrib(GL_TEXTURE_BIT)

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
[V2] Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>