libglademm will fail to compile in HB-0.9.2 unless is has a new
dep on :x11 to help it find its components. Add a `depends_on :x11`
Tested on Lion with clang and llvm from XCode-4.3.3.
ClosesHomebrew/homebrew#13469.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>