change lock format to let us detect and break stale locks. old style: symlink to pid new style: symlink to hostname:pid if lock code finds new-style lock, it breaks lock if locking pid is on same machine and pid is not alive. otherwise, lock is left alone. this makes locking code safe with old-style locks and with locks on other machines. new code makes server part of mercurial more robust in case machine crashes, power fails, or crazy user does kill -9.

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changeset:   1:9a79c33a9db3
tag:         tip
user:        a
date:        Thu Jan  1 00:00:00 1970 +0000
summary:     a

changeset:   0:01f8062b2de5
user:        b
date:        Thu Jan  1 00:00:00 1970 +0000
summary:     b