autoBeamOff bug

[Russ Ross]

There seems to be a bug in \autoBeamOff.  If it is issued in the
middle of a sequence of notes that would be beamed together, it
doesn't take effect until after the end of that group.  It seems that
the correct behavior should be to stop automatic beaming at the point
where the command is issued.  It poses a particular problem for me
with some (partially) generated input.

Here's an example showing the problem:

\version "2.5.15"
\score {
  \relative c' {
    \autoBeamOn d'8 cis d b cis b cis ais |
    b ais b d~ d \autoBeamOff cis d b |
  }
}

The final "d cis d b" sequence is beamed in the current code, but it
shouldn't be.

Thanks,

Russ