Add doctests to tox run

This is somewhat ugly since tox does not do shell-expansion so we have
to list all files with doctests in.  This is fine if new tests are
normally unittests however.

tox.ini

@@ -3,7 +3,11 @@ envlist = py26,py27
 
 [testenv]
 deps = nose
-commands = nosetests tests/
+commands =
+         nosetests tests/
+         nosetests --with-doctest eventlet/coros.py eventlet/event.py \
+             eventlet/pool.py eventlet/pools.py eventlet/proc.py \
+             eventlet/queue.py eventlet/timeout.py
 
 [testenv:py26selects]
 basepython = python2.6