T1686 - First patch to allow LilyPond Initialisation to use Guile V2 if required.

T1686 - First patch to allow LilyPond Initialisation to use Guile V2 if required.

lily/main.cc
1. add new conditional compilation blocks to call Guile V2 initialisation
if necessary.
2. add new routine to prefix new value to Guile list variable.
3. add new routines to generate environment variables for Guile V2.
4. add comment header for each routine/function.
lily/include/main.hh
1. declare new variable guile_major_version in main.cc external int

[dak, 2012-11-28 16:09:32]

http://codereview.appspot.com/6849088/diff/1/lily/main.cc
File lily/main.cc (right):

http://codereview.appspot.com/6849088/diff/1/lily/main.cc#newcode65
lily/main.cc:65: int guile_major_version = 2;
I don't think it makes sense to even define a guile_major_version since the
executable will only work with the version it has been compiled with.  So there
is no point in having a run-time decision criterion available.

http://codereview.appspot.com/6849088/diff/1/lily/main.cc#newcode296
lily/main.cc:296: /*
You have quite a few commits that "just" add comments to existing functions.  I
think it would make sense to commit these improvements of existing code as a
separate commit to staging.  No point really to have them go through a review
unless you are unsure whether some comment is correct (adding an incorrect
comment obviously is not an improvement).

If those are interspersed with other material in some commit, you can use

git checkout -p commit-id

to selectively pick out material from a given commit (in a different branch),
then do git commit to make a commit from the picked changes.