Show a better error message when user is already being followed

[ehabkost]

2010-02-04 23:45:33,797:DEBUG:passerd:got command: ('INVITE', '', ['botobr', '#twitter']) {}
2010-02-04 23:45:33,798:DEBUG:passerd:sending message: ('341', 'botoboto', 'botobr', '#twitter') {'prefix': 'passerd.server'}
2010-02-04 23:45:33,799:DEBUG:passerd:sending line: (':passerd.server 341 botoboto botobr #twitter',) {}
2010-02-04 23:45:35,020:DEBUG:twittytwister.twitter:hdrs: {'status': ['403 Forbidden'], 'content-length': ['178'], 'x-transaction': ['1265334334-34120-15362'], 'set-cookie': ['lang=en; path=/', '...], 'expires': ['Tue, 31 Mar 1981 05:00:00 GMT'], 'vary': ['Accept-Encoding'], 'connection': ['close'], 'server': ['hi'], 'x-revision': ['DEV'], 'last-modified': ['Fri, 05 Feb 2010 01:45:34 GMT'], 'x-runtime': ['0.06625'], 'pragma': ['no-cache'], 'cache-control': ['no-cache, no-store, must-revalidate, pre-check=0, post-check=0'], 'date': ['Fri, 05 Feb 2010 01:45:34 GMT'], 'content-type': ['application/xml; charset=utf-8']}
2010-02-04 23:45:35,021:DEBUG:twittytwister.twitter:hdrs end
2010-02-04 23:45:35,021:DEBUG:passerd:sending message: ('NOTICE', 'botoboto', ':error when trying to follow user: 403 Forbidden') {'prefix': 'passerd.server'}
2010-02-04 23:45:35,021:DEBUG:passerd:sending line: (':passerd.server NOTICE botoboto :error when trying to follow user: 403 Forbidden',) {}
2010-02-04 23:45:35,021:DEBUG:passerd:sending message: ('437', 'botoboto', 'botobr', ':Nick/channel is temporarily unavailable') {'prefix': 'passerd.server'}
2010-02-04 23:45:35,021:DEBUG:passerd:sending line: (':passerd.server 437 botoboto botobr :Nick/channel is temporarily unavailable',) {}