* scm/framework-tex.scm (font-load-command, define-fonts): Protect

* scm/framework-tex.scm (font-load-command, define-fonts): Protect
some TeX line ends with `%' to avoid additional horizontal space in
output.

* scripts/lilypond-book.py: Unexpand spaces to tabs.
(snippet_res): Use `x' modifier to represent regular expressions
in a friendlier way.
Fix `lilypond_block' for LaTeX to accept `%\end{lilypond}'.
(find_toplevel_snippets): Don't use indices from match group 0,
which is the whole pattern space, but group 1.