Previously, XKB_BINDIR was read inside a loop over the program
arguments, so was only read if it had arguments that weren't matched by
the first some number of checks.
The X server by default looks for it under its own prefix, which
isn't right. Not being able to run xkbcomp causes the Xkb keyboard
extension to fail (which incidentally is also the reason why
Ctrl-Alt-Fn didn't work).
svn path=/nixpkgs/trunk/; revision=8494
