Fix #1490.

Fix #1490.

Don't discard labels set on columns which are currently pruned or fall on
an empty barline.

* input/regression (page-label-loose-column.ly)

  new regtest, checks both unbreakable mid-line and empty barline labels

* lily/include/system.hh:

  add collect_labels ()

* lily/paper-column.cc (is_used):

  return true if 'labels is set

* lily/spacing-determine-loose-columns.cc (prune_loose_columns):

  set 'maybe-loose on columns which only contain page-labels

* lily/system.cc (break_into_pieces, collect_labels):

  collect labels from loose columns
  move label collection to separate method

[Neil Puttock, 2011-02-14 23:08:50]

Hi everybody,

This patch ensures page labels aren't ignored on mid-line unbreakable columns
(between notes inside a bar) and columns containing \bar "".

Please review.

Cheers,
Neil

[Graham Percival (old account), 2011-02-15 01:06:30]

LGTM

[Carl, 2011-02-15 01:22:35]

LGTM

Carl

[Graham Percival (old account), 2011-02-17 18:32:21]

Please push.