trivial Python code fixes in Plex

Cython/Plex/Machines.py

@@ -258,7 +258,8 @@ class FastMachine:
   def ranges_to_string(self, range_list):
     return string.join(map(self.range_to_string, range_list), ",")
   
-  def range_to_string(self, (c1, c2)):
+  def range_to_string(self, range_tuple):
+    (c1, c2) = range_tuple
     if c1 == c2:
       return repr(c1)
     else:

Cython/Plex/Regexps.py

@@ -122,7 +122,7 @@ class RE:
         beginning of a line. If nocase is true, upper and lower case
         letters should be treated as equivalent.
         """
-        raise exceptions.UnimplementedMethod("%s.build_machine not implemented" % 
+        raise NotImplementedError("%s.build_machine not implemented" % 
             self.__class__.__name__)
     
     def build_opt(self, m, initial_state, c):