Add feta-flags to build system (issue4662055)

[Carl . D . Sorensen]

Reviewers: Janek Warchol,

Message:
Here is a revision of Janek's patch to separate feta-flags from
feta-noteheads.

I believe that it works properly; I rebuilt the fonts and the flags look
fine.

To test, you will need to do

rm mf/out/* && make

before testing a lilypond file.

Description:
Add feta-flags to build system

Put noteheads and flags in different fonts, but have them both
built at the same time, so black_notehead_width can be common
across both files.

If either font changes, both will be rebuilt, but only one rebuild
should happen.

Please review this at http://codereview.appspot.com/4662055/

Affected files:
  M mf/GNUmakefile
  M mf/bigcheese.pe.in
  A mf/feta-flags-generic.mf
  A mf/feta-flags11.mf
  A mf/feta-flags13.mf
  A mf/feta-flags14.mf
  A mf/feta-flags16.mf
  A mf/feta-flags18.mf
  A mf/feta-flags20.mf
  A mf/feta-flags23.mf
  A mf/feta-flags26.mf
  M mf/feta-noteheads-generic.mf
  M mf/feta-noteheads-test-generic.mf
  M mf/feta-noteheads.mf
  M scripts/build/gen-emmentaler-scripts.py
  M scripts/build/mf-to-table.py