[Fontconfig] Cache and FAT

[Tor Lillqvist]

> I let our win32 hackers respond before making a decision either way.  Tor?

I just vaguely remember noticing before that looking at the mtime of a
directory indeed is not necessarily a reliable way to see if its
contents has changed on Windows. Unfortunately. So far I haven't
bothered doing anything to it, and just adviced people to run fc-cache
manually if it seems that they are missing fonts.

>> 1) scan directory and subdirectories and use max(mtimes, ctimes) of all
>>     files as mtime of directory.
>
> Would be a PITA.

But might still be the only (?) solution. Would be inside #ifdef
_WIN32 obviously.

--tml