bug#7890: `bzr status' errors prevent backing up edited file

[Glenn Morris]

Package: emacs
Version: 23.2
Severity: minor

I was editing files in my copy of the Emacs bzr repo.
The partition had plenty of space.
I hadn't noticed, but my home partition had filled up.
Emacs started failing to backup the files I was editing, saying:

  Cannot write backup file; backing up in /home/gm/%backup%~

I presume this was because `bzr status' was failing all the time
trying to write its trace file:

  File "/usr/local/lib/python2.6/dist-packages/bzrlib/trace.py", line
  188, in mutter _trace_file.write(out)
 IOError: [Errno 28] No space left on device

OK, this is a dumb failure mode for bzr, but IMO Emacs shoud be more
robust in the face of such an error. It's especially dumb for Emacs
to refuse to backup the file in a partition with plenty of space,
and instead to try to back it up to a full partition.