Fix syntax for Python 2.6 - no set literals.

IPython/utils/pyfile.py

@@ -1,23 +1,23 b''
 """Utilities for working with Python source files.
 
 Exposes various functions from recent Python standard libraries, along with
 equivalents for older Python versions.
 """
 import os.path
 
 try:    # Python 3.2
     from imp import source_from_cache, cache_from_source
 except ImportError:
     # Python <= 3.1: .pyc files go next to .py
     def source_from_cache(path):
         basename, ext = os.path.splitext(path)
-        if ext not in {'.pyc', '.pyo'}:
+        if ext not in ('.pyc', '.pyo'):
             raise ValueError('Not a cached Python file extension', ext)
         # Should we look for .pyw files?
         return basename + '.py'
     
     def cache_from_source(path, debug_override=None):
         if debug_override is None:
             debug_override = __debug__
         basename, ext = os.path.splitext(path)
         return basename + '.pyc' if debug_override else '.pyo'