Issue with symbol-list? and ly:parser-include-string

[Urs Liska]

As this thread suggested
https://lists.gnu.org/archive/html/lilypond-devel/2015-03/msg00193.html

there is an issue with the parser when a symbol-list? predicate is used 
as a function argument and ly:parser-include-string in that function.
As it turned out the problem is reproducible with very little effort, as 
you can see with the attached two files.

Obviously the symbol-list? predicate doesn't play well with 
ly:parser-include-string.

Some observations:

- it is not related to the \include command
  as you can see from the two alternative strings passed to 
ly:parser-include-string
- The error messages are very different depending on what comes after 
the function call
- Obviously the problem is in determining when the symbol-list? is 
completed, i.e. in the look-ahead
- In the (more complex) original context there are even other error 
messages.
- when there is any Scheme expression (the #(display "") in the example, 
but a #(define foo 'bar) works
  just the same) parsing works properly but LilyPond statements cause 
the parser to fail

main.ly
Description: Text Data

included.ily
Description: Text document