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

[Carl . D . Sorensen]

Reviewers: ,

Message:
Benjamin has sent a revised patch that addresses Neil's concerns.

Please review the patch.

THanks,

Carl


Description:
fix ly:parser-parse-file in an ly file
This switches to using the flex buffer stack.

Please review this at http://codereview.appspot.com/1345041/show

Affected files:
  A input/regression/include-string.ly
  M lily/includable-lexer.cc
  M lily/include/includable-lexer.hh
  M lily/include/lily-parser.hh
  M lily/lexer.ll
  M lily/lily-parser-scheme.cc
  M lily/lily-parser.cc