commands: make backout acquire locks before processing Before this patch, "hg backout" executes below before acquisition of wlock. - cmdutil.checkunfinished() - cmdutil.bailifchanged() - repo.dirstate.parents() It may cause unintentional result, if another command runs parallelly (see also issue4368). In addition to it, "hg backout" refers changelog for purposes below without acquisition of store lock (slock), and it may cause unintentional result, if store is updated parallelly. - show and update to the revision by 'repo.changelog.tip()' - examine for "created new head" by 'repo.branchheads()' and 'cmdutil.commitstatus()' To avoid this issue, this patch makes "hg backout" acquire wlock and slock before processing.