Build dependencies for metafont files (issue 779).

Build dependencies for metafont files (issue 779).

Write .dep files containing make dependency rules for .mf files,
allowing to simply type `make' to process the fonts after changing
an input'ed file and have the fonts updated with the minimum amount
of processing.

These .dep files are generated by recursively scanning for lines
of the form "input X;" in the .mf files, and looking up these
input'ed files within the mf source directory. The .dep files are
included into the build by stepmake/generic-targets.make.

http://code.google.com/p/lilypond/issues/detail?id=779

[Julien Rioux, 2013-09-12 16:22:07]

Please review.

[janek, 2013-09-14 10:22:22]

I'm not familiar with build system, but from the comments the patch looks good
(and i'm very happy to see this fixed!)

thanks,
Janek