mesa: In CopyTexSubImage, use matching format for Z32_FLOAT_X24S8 textures.

The meta path for CopyTexSubImage operates by reading the source image
to a temporary buffer using glReadPixels and then uploading it to the
texture using TexSubImage.  This patch ensures that when the texture
format is MESA_FORMAT_Z32_FLOAT_X24S8, we use the proper image type
for the temporary buffer (GL_FLOAT_32_UNSIGNED_INT_24_8_REV).

Fixes some failures with piglit tests "copyteximage
{1D,2D,CUBE,RECT,2D_ARRAY}".
i965/gen6+: Fix copying of stencil images in blorp CopyTexSubImage path.

When handling the depth/stencil case of CopyTexSubImage using blorp,
we weren't paying attention to intel_mipmap_tree::stencil_mt field; as
a result we were sometimes attempting to read and/or write stencil
data using the depth miptree, resulting in image corruption.

Fixes some failures with piglit tests "copyteximage
{1D,2D,CUBE,RECT,2D_ARRAY}".
i965/gen6+: Fix multisample assertions in CopyTexSubImage hw blitter path.

Commit 045612c (intel: Add an assert for glCopyTexSubImage() being
called on MSAA buffers) added an assertion to intel_copy_texsubimage()
to make sure that multisampling was not in use, based on the
assumption that glCopyTexSubImage() can't legally be used with
multisampling.

However, there is one case where glCopyTexSubImage() can legally be
used with multisampling: when the source buffer is a multisampled
window system buffer.  If the source and destination color formats
don't match, the blorp path will fail, so intel_copy_texsubimage()
will be called.  In this case, we need intel_copy_texsubimage() to
return false so that we fall back to meta to do the copy.  (The
multisampled source buffer won't cause a problem for the meta path,
because it uses glReadPixels, which forces a multisample resolve).

It's still safe to assert that the destination image is
single-sampled, because it's not legal to call glCopyTexSubImage() on
multisampled textures.

Fixes some failures with piglit tests "copyteximage
{1D,2D,CUBE,RECT,2D_ARRAY}" (with "samples=..." argument).