Return server capabilities (RFC 2449) as a dictionary
>>> c=poplib.POP3('localhost')
>>> c.capa()
{'IMPLEMENTATION': ['Cyrus', 'POP3', 'server', 'v2.2.12'],
'TOP': [], 'LOGIN-DELAY': ['0'], 'AUTH-RESP-CODE': [],
'EXPIRE': ['NEVER'], 'USER': [], 'STLS': [], 'PIPELINING': [],
'UIDL': [], 'RESP-CODES': []}
>>>
Really, according to RFC 2449, the cyrus folks should avoid
having the implementation split into multiple arguments...