Limit tuplet bracket length to actual tuplet length

Limit tuplet bracket length to actual tuplet length

See the regtest for an example of the problem.  Without the patch, the
tuplet bracket extends over all of

  \tuplet 3/2 4 { g16 a b } c8

including c8, resulting in visual lengths not adding up.

[lemzwerg, 2014-09-04 18:03:41]

LGTM.

[dak, 2014-09-05 10:27:15]

Catch overlong durations while in process_music