Python 3 preparation: convert exec to a function.

Tool-generated patch.

Author: jsm28

roundup/cgi/PageTemplates/PythonExpr.py

@@ -31,7 +31,7 @@ def __init__(self, name, expr, engine):
         self.expr = expr = expr.strip().replace('\n', ' ')
         try:
             d = {}
-            exec 'def f():\n return %s\n' % expr.strip() in d
+            exec('def f():\n return %s\n' % expr.strip(), d)
             self._f = d['f']
         except:
             raise CompilerError(('Python expression error:\n'