Add some includes for makeinfo. Fixes build of documentation.

Add some includes for makeinfo.  Fixes build of documentation.

LANG= makeinfo --enable-encoding -I./out-www --output=out-www/lilypond-internals.info out-www/lilypond-internals.texi
out-www/lilypond-internals.texi:12: @include `macros.itexi': No such file or directory.
out-www/lilypond-internals.texi:858: Unknown command `q'.
...
out-www/lilypond-internals.texi:8910: Misplaced {.
out-www/lilypond-internals.texi:8910: Misplaced }.
Too many errors!  Gave up.
make[7]: *** [out-www/lilypond-internals.info] Error 1
make[7]: Leaving directory `/home/janneke/vc/gub/target/linux-64/build/lilypond-git.sv.gnu.org--lilypond.git-master/Documentation/user'
make[6]: *** [WWW-1] Error 2