Re: Improves horizontal spacing of axis groups that SpanBar grobs traverse. (issue 4917046)

[pkx166h]

ok, this passes make but I get a lot of reg tests show up but I cannot
see any diffs at all (i.e no 'green' shadows that indicate the changes).
Either it's unbelievably subtle or something else is triggering the reg
tests to show up. They are to big to post them all here but he diffs
that show up are

bar-extent.ly
tablature-tie-behaviour.ly
slur-cross-staff.ly
volta-multi-staff.ly
volta-multi-staff-inner-staff.ly
tablature-grace-notes.ly
span-bar-partial.ly
double-repeat.ly
spanner-alignment.ly
beam-cross-staff.ly
palm-mute.ly
bar-line-segno.ly
dead-notes.ly
context-nested-staffgroup.ly
tablature-glissando.ly
spacing-knee-compressed.ly
beam-cross-staff-slope.ly
slur-extreme.ly
note-line.ly
span-bar-break.ly
voice-follower.ly
cluster-cross-staff.ly
auto-change.ly
page-spacing-staff-group-nested.ly
tablature-harmonic-tie.ly
remove-empty-staves-auto-knee.ly
grace-staff-length.ly
span-bar-spacing.ly
arpeggio-span-collision.ly

etc.

Not all but a *lot*

So I don't know if this needs more work or not really, but am putting
this as 'review' for those that know better than I.

http://codereview.appspot.com/4917046/