Bug: Autobeam doesn't end if short notes are at the end.

[Reino Ruusu]

> i'm not top-posting

Autobeaming produces beams that do not obey the rules, if the part prior to the
ending moment does not contain short notes.

Example:

\layout {
indent=0\pt
ragged-right=##t
}

\relative c' { c8 c c c16 c }

This produces a beam that spans all five notes, although an ending is specified
for 4/16'ths. This is because the auto-beam-engraver only considers notes that
occur prior to the potential ending moment.

When a shorter note is processed by acknowledge_stem(), all earlier moments
should be rechecked for applicable beaming rules.

-- 
Reino