Added a "replace" method to lockhandler, courtesy of patch by user Shell.

src/locks/lockhandler.py

@@ -290,6 +290,16 @@ class LockHandler(object):
         self.log_obj = None
         return True
 
+    def replace(self, lockstring, log_obj=None):
+        "Replaces the lockstring entirely."
+        old_lockstring = str(self)
+        self.clear()
+        try:
+            return self.add(lockstring, log_obj)
+        except LockException:
+            self.add(old_lockstring, log_obj)
+            raise
+
     def get(self, access_type):
         "get the lockstring of a particular type"
         return self.locks.get(access_type, None)