Add a --disable-locking option to svnsync.
Add a --disable-locking option to svnsync.

The built-in locking of svnsync has a known race condition (see issue #3546).
This option allows those who'd rather use an external locking mechaninism
(such as tools like flock and lockfile) to disable svnsync's internal locking
entirely. This avoids associated network overhead, and stale locks in case the
network connection drops unexpectedly.

* subversion/svnsync/main.c
  (svnsync__opt): Add svnsync_opt_disable_locking.
  (svnsync_cm): Enable the new --disable-locking option for the
   init, sync, and copy-revprops subcommands.
  (svnsync_options): Document --disable-locking option.
  (opt_baton_t): New field 'disable_locking'.
  (initialize_cmd, synchronize_cmd, copy_revprops_cmd): Don't use
   locking if the --disable-locking option was passed.
  (main): Pass the --disable-locking option into the opt baton.

Patch by: Jon Foster <Jon.Foster@cabot.co.uk>
          me

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion