* Documentation/user/GNUmakefile (LILYPOND_BOOK_FLAGS): be anal

* Documentation/user/GNUmakefile (LILYPOND_BOOK_FLAGS): be anal
with type checks.

* Documentation/GNUmakefile (LILYPOND_BOOK_FLAGS):
* input/regression/GNUmakefile (LILYPOND_BOOK_FLAGS):
* input/test/GNUmakefile (LILYPOND_BOOK_FLAGS):
* Documentation/user/invoking.itexi:
* lily/scm-option.cc:
* lily/main.cc: Debugging options: ly-set-option (was:
set-lily-option).

* lily/scm-option.cc (ly_option_usage): New function.