Include another file in a score

[pinobatch]

Eventually a Pently score may grow bigger than a single file. This may happen if you have different people working on the sound effects and music, or if you are using ft2pently for the music and a handmade score for the sound effects. So in order to avoid having to cat the input files together, I'd recommend adding include to a score, so that the master file can include the sound effects and then the output of ft2pently.

Sub-tasks:

• Convert all linenum variables to path, linenum
• Ensure exception and warning handler can see the entire stack of open files