Python 2.3 fix.

Cython/Build/Dependencies.py

 from glob import glob
 import re, os, sys
+from cython import set
 
-try:
-    set
-except NameError:
-    # Python 2.3
-    from sets import Set as set
 
 from distutils.extension import Extension
 

Cython/Build/Inline.py

 import tempfile
 import sys, os, re, inspect
+from cython import set
 
 try:
     import hashlib

Cython/Shadow.py

@@ -188,15 +188,11 @@ except NameError: # Py3
 py_float = float
 py_complex = complex
 
+
 try:
-    # Python 3
-    from builtins import set, frozenset
-except ImportError:
-    try:
-        # Python 2.4+
-        from __builtin__ import set, frozenset
-    except ImportError:
-        # Py 2.3
+    set
+except NameError:
+    # Python 2.3
     from sets import Set as set, ImmutableSet as frozenset
 
 # Predefined types