setup.py: Use setuptools for bdist_wheel

Solves this problem:

```
(responsesvc)marca@marca-mac2:~/dev/git-repos/greenlet$ python setup.py bdist_wheel
usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
   or: setup.py --help [cmd1 cmd2 ...]
   or: setup.py --help-commands
   or: setup.py cmd --help

error: invalid command 'bdist_wheel'
```