MIPS: Fix exported symbols in public API.
create_bits(): Cast the result of height * stride to size_t

In create_bits() both height and stride are ints, so the result is
also an int, which will overflow if height or stride are big enough
and size_t is bigger than int.

This patch simply casts height to size_t to prevent these overflows,
which prevents the crash in:

    https://bugzilla.redhat.com/show_bug.cgi?id=972647

It's not even close to fixing the full problem of supporting big
images in pixman.

See also

    https://bugs.freedesktop.org/show_bug.cgi?id=69014
configure.ac: Check if the compiler supports GCC vector extensions

The Intel Compiler 14.0.0 claims version GCC 4.7.3 compatibility
via __GNUC__/__GNUC__MINOR__ macros, but does not provide the same
level of GCC vector extensions support as the original GCC compiler:
    http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html

Which results in the following compilation failure:

In file included from ../test/utils.h(7),
                 from ../test/utils.c(3):
../test/utils-prng.h(138): error: expression must have integral type
      uint32x4 e = x->a - ((x->b << 27) + (x->b >> (32 - 27)));
                            ^

The problem is fixed by doing a special check in configure for
this feature.
Pre-release version bump to 0.32.6
Post-release version bump to 0.32.7