Re: Creates a LeftBarStub that stops lyrics from bumping into the SystemStartBar. (issue 5201043)

[mtsolo]

This new patch set eliminates all regtest diffs via a mechanism that
allows extremal lyrics to be flush with the left edge.
It kinda sorta bends LilyPond into doing something it is not designed to
do :: returning pureY-extents for items that are dependent on the start
and end positions (normally, only spanner Y-extents change based on
start and end positions).  The logic is that a LeftBarStub should have a
Y-extent iff it is at the beginning of a staff and if said staff will
not bump into a SystemStartBar.  Knowing if it will bump into a
SystemStartBar can only be done if we know which staves are alive and
which staves are hara-kiri'd, which'll change based on the start / end
in question.

This seems like the sorta thing that'd slow down lilypond, so I'd
appreciate it if people tested it on pieces with lots-o-lyrics!

Cheers,
MS

http://codereview.appspot.com/5201043/