Fix 1816: Lilypond-Book: don't clear the auto-detected line-with, rather modify it (issue 4888046)

[percival . music . ca]

Thanks so much for looking into this!


http://codereview.appspot.com/4888046/diff/1/python/book_snippets.py
File python/book_snippets.py (left):

http://codereview.appspot.com/4888046/diff/1/python/book_snippets.py#oldcode424
python/book_snippets.py:424: if type == 'lilypond':
This part is only executed if we do not have a line width (line 404).
But I thought we were getting the line width from latex?  Does that info
not get stored in self.option_dict for some reason?

I'm content to trust you that it works, but I'm having trouble following
the logic of has_line_width and self.option_dict[LINE_WIDTH].

http://codereview.appspot.com/4888046/