fast_bilinear_cover_init: Don't install a finalizer on the error path

No memory is allocated in the error case, so a finalizer is not
necessary, and will cause problems if the data pointer is not
initialized to NULL.
Merge branch 'master' of git://anongit.freedesktop.org/git/pixman
iwmmxt: Disallow if gcc version is < 4.8.

Later versions of gcc-4.7.x are capable of generating iwMMXt
instructions properly, but gcc-4.8 contains better support and other
fixes, including iwMMXt in conjunction with hardfp. The existing 4.5
requirement was based on attempts to have OLPC use a patched gcc to
build pixman. Let's just require gcc-4.8.
Make the first argument to scanline fetchers have type bits_image_t *

Scanline fetchers haven't been used for images other than bits for a
long time, so by making the type reflect this fact, a bit of casting
can be saved in various places.
Drop support for 8-bit precision in bilinear filtering

The default has been 7-bit for a while now, and the quality
improvement with 8-bit precision is not enough to justify keeping the
code around as a compile-time option.
Merge branch 'master' of https://github.com/johne53/MB3Pixman
Merge branch 'master' of git://anongit.freedesktop.org/git/pixman