[Fontconfig] Greatly improved subpixel filtering in Xft

[Anders Kaseorg]

Well, here's a first attempt at making the filter configurable:
   <http://www.kaseorg.com/~anders/libXft-improved-filtering.patch>

Set Xft.filtertype: 0 in /etc/X11/Xresources for the my inter-pixel 
filter, 1 for the existing intra-pixel filter. (Yeah, my filter is the 
default for now.) New filters can be added in xftglyphs.c, and will 
accessible by setting filtertype to their index. I wasn't sure whether 
the setting should have been XFT_BLAH or FC_BLAH, but I made it 
XFT_FILTER_TYPE because I didn't want to muck around with fontconfig too.

It works great for the most part, but there seems to be a problem: the 
setting isn't getting applied in gnome-terminal, even though it is 
applied in gedit with the same font. I'm not sure why that would be.

Anders