This implements function decorators using the
Java-style syntax described in
http://mail.python.org/pipermail/python-dev/2004-June/045516.html

As the patch changes the grammar, you'll need to
make sure Include/graminit.h and Python/graminit.c
are writable after applying the patch but before
compiling (after a standard CVS checkout they are
read-only, which stops pgen from working).

Changes: 

   - adding @ as a token
   - changing the grammer for funcdef
   - adding com_decorator in compile.c
   - adding test_decorator.py (based on Guido's version)