inotify: don't fall over just because of a dangling symlink
Previously, the inotify server failed to start if .hg/inotify.sock was
a symlink that pointed to a non-existent path. This behaviour does not
seem to make any sense.
Now, if we encounter a broken symlink, we unlink it and continue.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state