Avoid a division-by-zero exception if the first number returned by
rand() is a multiple of 500, causing us to create a zero width pixmap,
and then attempt to use get_rand(0) when generating a random stride...
Fixes https://bugs.freedesktop.org/attachment.cgi?id=34162
Instead of mucking around with CFLAGS in configure.ac, preventing
users from setting their own CFLAGS, just define the
PIXMAN_USE_INTERNAL_API and PIXMAN_DISABLE_DEPRECATED in
pixman-private.h
Bug 22844 demonstrates that it is not sufficient to play tricks with
the clip regions to work around the bogus images from the X
server. The problem there is that if the operation hits the general
path and the destination has a different format than a8r8g8b8, the
destination pixels will be fetched into a temporary array. But because
those pixels would be outside the clip region, they would be fetched
as black. The previous workaround was relying on fast paths fetching
those pixels without checking the clip region.
In the new scheme we work around the problem at the
pixman_image_composite() level. If an image is determined to need a
work around, we translate both the bits pointer, the coordinates, and
the clip region, thus effectively undoing the X server's broken
computation.
