Move left-broken line-spanner check to callback.

Move left-broken line-spanner check to callback.

Currently, left-broken line spanners and hairpins are removed when they
end on the first note of the new system.  Though this is appropriate
for glissandi and voice followers, there is no way to override this
default behaviour.

This patch allows the user to tweak the appearance by overriding
'after-line-breaking.

- removed left-broken check from ly:line-spanner::print to a new
after-line-breaking callback, ly:spanner::after-line-breaking

- removed hairpin after-line-breaking callback and associated method
consider_suicide ()

- added new callback to Hairpin, Glissando and VoiceFollower

[joeneeman, 2009-04-08 20:42:51]

One minor comment, otherwise lgtm

http://codereview.appspot.com/32148/diff/1/7
File lily/spanner.cc (right):

http://codereview.appspot.com/32148/diff/1/7#newcode426
Line 426: Spanner::after_line_breaking (SCM grob)
Can you think of a name that describes what the function actually does? Like
Spanner::suicide_if_spanned_time_is_empty, but maybe less verbose...

[Neil Puttock, 2009-04-11 12:31:10]

On 2009/04/08 20:42:51, joeneeman wrote:
> http://codereview.appspot.com/32148/diff/1/7#newcode426
> Line 426: Spanner::after_line_breaking (SCM grob)
> Can you think of a name that describes what the function actually does? Like
> Spanner::suicide_if_spanned_time_is_empty, but maybe less verbose...

How about Spanner::kill_zero_length_span or Spanner::kill_zero_spanned_time?

[joeneeman, 2009-04-11 19:22:54]

On 2009/04/11 12:31:10, Neil Puttock wrote:
> On 2009/04/08 20:42:51, joeneeman wrote:
> > http://codereview.appspot.com/32148/diff/1/7#newcode426
> > Line 426: Spanner::after_line_breaking (SCM grob)
> > Can you think of a name that describes what the function actually does? Like
> > Spanner::suicide_if_spanned_time_is_empty, but maybe less verbose...
> 
> How about Spanner::kill_zero_length_span or Spanner::kill_zero_spanned_time?

I prefer the second one.

[Neil Puttock, 2009-04-13 14:41:05]

On 2009/04/11 19:22:54, joeneeman wrote:

> I prefer the second one.

OK, ly:spanner::kill-zero-spanned-time it is.

I've added a convert rule just in case anybody's using
ly:hairpin::after-line-breaking.