tryimportone: use dirstateguard instead of beginparentchange/endparentchange To fix the issue that the recent (in memory) dirstate isn't visible to external process (e.g. "precommit" hook), a subsequent patch makes "localrepository.commit()" invoke "dirstate.write()" in it. This change will make "beginparentchange()" and "endparentchange()" on dirstate in "cmdutil.tryimportone()" meaningless, because: - "dirstate.write()" writes changed data into ".hg/dirstate", but - aborting between "beginparentchange()" and "endparentchange()" doesn't cause any restoring ".hg/dirstate" it just discards changes in memory. This patch uses "dirstateguard" instead of "beginparentchange()" and "endparentchange()" in "cmdutil.tryimportone()" to restore ".hg/dirstate" during a failure even if "dirstate.write()" is executed before a failure. This patch uses "lockmod.release(dsguard)" instead of "dsguard.release()", because processing may be aborted before assignment to "dsguard" , and the "if dsguard" examination for safety is redundant.