[Fontconfig] commit: configurable per-directory cache dirs

[Patrick Lam]

Some time ago, keithp wrote a patch which made /var/cache/fontconfig 
configurable.  I had reviewed it but wanted to re-review it. 
Unfortunately I never got a chance to re-review it and it just sat 
there.  I've committed it to branch now.  I think there was one issue to 
take care of: sudo fc-cache had the improper behaviour because HOME was 
not set for root.  I'll take a look at that later today, as well as 
miscellaneous stuff that people have posted.

pat