bdftopcf specifically will not read symbolic links. This causes it to
fail when creating the programs/fontaliases/*/C/dtinfo.pcf.Z file and
subsequently, the fonts.dir file.
So, we add a new Imake macro: CopySourceFile(), to copy rather than
symlink the dtinfo.bdf file so these operations can complete
successfully. The dtinfo.bdf file is only 5KB, so there's very little
impact having an extra copy created during a build.
