[Fontconfig] A couple of very old patches

[Keith Packard]

I'm packaging fontconfig 2.9.0 for debian today and found a couple of
ancient patches in my local tree.

The first patch, [PATCH 1/2] Use posix_fadvise to speed startup,
should improve startup time for the first application using fontconfig
by asking the kernel to queue reads of the entire font cache.

The second patch, [PATCH 2/2] Use const more often, just sticks
'const' declarations in a few more places within the implementation.

These have been rebased on top of 2.9.0.

-keith