Suggestion: Keep original breaks

[Urs Liska]

Hi all,

I would like to suggest an enhancement in the handling of line breaks 
that is useful for copying scores from existing models.
Currently LilyPond can decide about breaks herself or we can manually 
force or prevent breaks.
But when copying from or proof-reading against an existing score it is 
practical to have the original breaks present for this stage but not for 
the actual resulting score.
Therefore I suggest a new set of commands \originalBreak, 
\originalPageBreak and \originalPageTurn that make this process more 
automatic by conditionally outputting the respective break or nothing, 
depending on the presence of a switch.

I suggest a command line option -dkeep-original-breaks for this switch. 
That way the user can add that option for a compilation or write 
"#(ly:set-option 'keep-original-breaks)" in the input file.

I have a patch that does this and works well.
If you agree that this is a useful idea and don't have better ideas 
about naming or how the switch is implemented I would add the respective 
documentation and upload the patch for review.

Any opinions?
Thanks
Urs