[Fontconfig] commit (branch): read and write cache files.

[Patrick Lam]

Hi all,

I've just committed another revision to my branch.  This revision
includes support for reading and writing to an mmap file: if you run
fc-cache, then it creates this mmap file, and running fontconfig-using
programs uses the mmap file.  Here's what valgrind fc-match --sort tells me:

==22708== LEAK SUMMARY:
==22708==    definitely lost: 0 bytes in 0 blocks.
==22708==      possibly lost: 0 bytes in 0 blocks.
==22708==    still reachable: 17719 bytes in 904 blocks.
==22708==         suppressed: 0 bytes in 0 blocks.
==22708== Reachable blocks (those to which a pointer was found) are not
shown.
==22708== To see them, rerun with: --show-reachable=yes

(fc-list is even better, it loses 3200 bytes and has 2017 bytes still
reachable).

The normal one, by contrast, does this:

==22748==
==22748== LEAK SUMMARY:
==22748==    definitely lost: 0 bytes in 0 blocks.
==22748==      possibly lost: 0 bytes in 0 blocks.
==22748==    still reachable: 115649 bytes in 1525 blocks.
==22748==         suppressed: 0 bytes in 0 blocks.
==22748== Reachable blocks (those to which a pointer was found) are not
shown.
==22748== To see them, rerun with: --show-reachable=yes

Currently it writes the mmap file to /tmp, but this will change soon.  I
noticed that currently fontconfig writes cache files to directories
containing fonts, plus a global one on a per-user basis in
~/.fonts.cache.  Is there an appropriate place to put a global cache file?

pat