Enhancements on Issue 659: alternate segno symbol (issue181144)

[Marc Hohl]

Hello all,

I have uploaded some enhancements due to Alexander Kobel's proposals.
The first attempt to upload broke on my console with some error messages,
so I did it again - now I see that I uploaded two identical versions.
And furthermore, the changes to scm/tablature.scm which Carl had pushed
already are in this patch set, too, due to a missing "git pull" just before
rebasing, so I uploaded another version.

It would be fine to calculate the width of the segno stencil automatically,
but I hardcoded the value, so it seems to work fine.

Is the changed definition of the double bar line correct?

Thanks in advance,

Marc

http://codereview.appspot.com/181144