Improve get_lock() performance in case we are just checking for a lock to potentially exist. If it may not exist, we don't need to create an error object but can simply return a NULL lock. Also, having no lock file at all is a common case, hence check for it.
Improve get_lock() performance in case we are just checking
for a lock to potentially exist. If it may not exist, we don't
need to create an error object but can simply return a NULL
lock. Also, having no lock file at all is a common case, hence
check for it.

* subversion/libsvn_fs_fs/lock.c
  (get_lock): add must_exist parameter; optimize checks
  (get_lock_helper, unlock_body): adapt callers

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1346084 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion