waiter decorater implemented
_auth_me is now re-entrant

if it is called multiple times before the first call doesn't return
it is called only once
CachingAuthenticator uses wait decorator

instead of manually taking care waiters
removed unnecessary code
Changed wait signature - thanks @radix

It now takes optional list of keyword arguments to ignore instead of
ignoring all kwargs earlier
using updated wait decorator
clearer sentence - thanks @radix
Merge branch 'master' into auth-waiters

Conflicts:
	otter/auth.py
not using Deferred - lint fix
Merge pull request #802 from rackerlabs/auth-waiters

Wait decorator to disallow re-entrantcy