bug#8207: 24.0.50; undo in indirect buffer leaves stale file lock symlink

[Stephen Berman <stephen.berman@gmx.net>]

1. emacs -Q
2. Visit some file, e.g. "foo".
3. M-: (switch-to-buffer (make-indirect-buffer (current-buffer) "bar"))
4. In the indirect buffer "bar" do something to modify the buffer,
   e.g. type SPC.  This causes a file lock symlink like the following to
   be added to the directory containing "foo":
   .#foo -> steve@escher.fritz.box.800:1299574078
5. Type `C-_' to undo the change in step 4, so that "bar" is now
   unmodified, and then kill "bar".
=> The file lock symlink in foo's directory is still there.  

If instead of undoing the change in step 5 the file had been saved, then
the lock would have been released and the symlink deleted.  In fact,
this is the only way, aside from deleting it manually, to eliminate the
symlink.  But if a change is undone, the file is unmodified and hence
cannot be saved, so the symlink should be deleted in this case.

In GNU Emacs 24.0.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2011-03-08 on escher
Windowing system distributor `The X.Org Foundation', version 11.0.10800000
configured using `configure  '--without-toolkit-scroll-bars' 'CFLAGS=-g -O2 -fno-optimize-sibling-calls''