Node names can't have backslashes

[Carl D. Sorensen]

Jean-Charles,

Your latest commit adds backslashes back into the node name.

We had a recent discussion on the problems of having
backslashes in node names:

http://thread.gmane.org/gmane.comp.gnu.lilypond.devel/16894

The result of the discussion was a determination that if
section names had a backslash, the node name would be the
section name without a backslash.  So I think the node name
was correct before the backslash was added.

Thanks,

Carl