pygtk-2.24.0 on Lion will not compile because it can't find
`<pango/pangocairo.h>. This occurs because pkgconfig has trouble
querying the pangocairo.pc module because it complains that a
required module, `fontconfig` can't be found and suggests adding
it's path to `PKG_CONFIG_PATH`. We know `fontconfig` is a part
of X11. So add `depends_on :x11` to the formula so that all the
pkgconfig modules can be located.
Tested by importing pygtk, importing cairo, and by running
`brew test -v pygtk` on Lion with clang and llvm from XCode-4.3.3.
FixesHomebrew/homebrew#13205 and possibly Homebrew/homebrew#13256ClosesHomebrew/homebrew#13257.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>
