rhg: Initial repository locking...
rhg: Initial repository locking
Initial Rust implementation of locking based on the `.hg/wlock` symlink (or file),
with lock breaking when the recorded pid and hostname show that a lock was
left by a local process that is not running anymore (as it might have been
killed).
Differential Revision:
https://phab.mercurial-scm.org/D11835
