keep git master clean

[Graham Percival]

We have a lot of newbie contributors now.  That's great!  However,
newbie contributors aren't confident, and aren't able to figure
out why the build is failing.  Especially when they're trying to
build lilypond for the first time, and automatically assume that
if git master can't build it's their fault.

To anybody with git push ability: keep your maoing garbage off of
git master.  It's not fair to our young ones.  This has happened
half a dozen times in the past few months.  That's half a dozen
times too many.

To anybody else with git push ability: if git master cannot
compile -- either with "make" or "make doc" -- then revert the
problematic commit.  Don't politely ask the committer to fix it.
Don't politely ask if there's a problem and start discussing it.
Revert the maoing commit, and *then* start discussing how to fix
it on -devel.
(but make certain that the commit is actually bad -- if you
suspect a build problem, then try rebuilding from scratch)

If somebody reverts one of your commits, don't take it personally.
We're just trying to let new contributors get started.


Carl: I killed your 713aeac92c2bd06a9ae0ed38d13f4b20fba3f9a8 which
was the regtest for 1440.  Dunno why it was failing; building it
from the command-line worked fine.

Cheers,
- Graham