revset: use list instead of tuple for compatibility with python before 2.6

'string elements'.split() instead of explicitly typing a list of strings is
used. This is done in other parts of Mercurial code, too.

mercurial/revset.py

@@ -952,8 +952,8 b' def matching(repo, subset, x):'
     # We may want to match more than one field
     # Not all fields take the same amount of time to be matched
     # Sort the selected fields in order of increasing matching cost
-    fieldorder = ('phase', 'parents', 'user', 'date', 'branch', 'summary',
-        'files', 'description', 'substate',)
+    fieldorder = ('phase parents user date branch summary files description'
+                  ' substate').split()
     def fieldkeyfunc(f):
         try:
             return fieldorder.index(f)