* Documentation/user/GNUmakefile ($(outdir)/lilypond/source,

* Documentation/user/GNUmakefile ($(outdir)/lilypond/source,
$(outdir)/music-glossary/source): Fixes for `make -j'.

* Documentation/user/introduction.itely: Don't let images overlap
and update its scaling values.

* Documentation/user/lily-flat-bw.png,
Documentation/user/henle-flat-gray.png: Add vertical whitespace:
texinfo doesn't center images vertically for PDF output.