Merge mkfontdir into mkfontscale

I've attempted to preserve all the relevant portions of the history from xorg/app/mkfontdir while merging into the mkfontscale Makefile.am & configure.ac so that builds work along the way - despite the churn along the way, the final state is a small change to the mkfontscale repo beyond the addition of mkfontdir.in and mkfontdir.man.