somewhat esoteric bug with grace notes and key changes

[Graham Percival]

Here's a bug that doesn't occur very often; it might not be worth the time
to fix it.  But here it is...

This file works as expected.  But when you uncomment the \grace line, the
piece begins in treble clef, has three grace notes, and _then_ executes
the \global section (time signature, key change, etc).

I can work around it by inserting a "\partial 32 s32" between the beginning
of \melody and the "a4 a" notes, but it looks like an ugly hack.  My .ly file
would look much nicer if I didn't need to do that.  :)

Tested on recent CVS of 1.7.19 on a mostly Debian/testing box (some stuff from
unstable, include TeX, mftrace, and some other lilypond-related programs).

----
global = \notes {
\time 2/4 \clef bass \key d \major
}
melody = \notes{
%\grace {[cis'16 b]}
a4 a |
}
\score{ \context Staff <
\global
\melody
>}
----

Cheers,
- Graham