* lily/slur-scoring.cc (generate_avoid_offsets): new

* lily/slur-scoring.cc (generate_avoid_offsets): new
function. Generate avoid offsets once per slur.

* lily/slur.cc (add_extra_encompass): add dependency to
extra-encompass object. This fixes bugs/c-phrasing-slur.ly

* scripts/lilypond-book.py (do_options): --psfonts doesn't take
argument anymore.

* scripts/lilypond-book.py (set_default_options): new
function. Call this before dissecting snippets, so linewidth
settings reach the snippets.