This fixes a bug with relative paths as arguments when 'autochdir' was
enabled and also cuts down on startup times. However, it also has the
negative side-effect that 'f' is no longer supported in 'guioptions'.
Instead of checking for Ctrl-character, check when Cocoa translates a
keypress to an unprintable character (in particular, this happens on
Ctrl-character). This ensures keys like <C-]> work on (some) keyboards
where ] requires the use of Alt.