locking.LockSet: don't modify input arguments

Currently LockSet.acquire() sorts in place it's input argument if it's a
list. This is not good, since callers might depend on a specific
ordering of the input data, and this is a 'hidden' modification.

We fix it by simply using a sorted copy, instead of sorting in place.

Reviewed-by: ultrotter

lib/locking.py

@@ -451,7 +451,7 @@ class LockSet:
       if isinstance(names, basestring):
         names = [names]
       else:
-        names.sort()
+        names = sorted(names)
 
       acquire_list = []
       # First we look the locks up on __lockdict. We have no way of being sure