Re: fix ly:parser-parse-file in an ly file (issue1345041)

[dak]

 > Note that this description isn't correct anymore. This patch doesn't
> actually prevent those functions from segfaulting but adds a new
> interface ly:parser-include-string. I think ly:parser-parse-string and
> ly:parser-parse-file should actually be banned in .ly files.

If ly:parser-include-string offers all the functionality of
ly:parser-parse-string and ly:parser-parse-file, the latter should be
implemented in terms of the former (rather than segfaulting in some
situations) for compatibility.

If it doesn't offer all functionality, banning the old functions without
offering a substitute seems like a bad thing to do to the user.

http://codereview.appspot.com/1345041/show