SleekTest can now use matchers when checking stanzas, using
the method parameter for self.check(), self.recv(), and self.send():
method='exact' - Same behavior as before
'xpath' - Use xpath matcher
'id' - Use ID matcher
'mask' - Use XML mask matcher
'stanzapath' - Use StanzaPath matcher
recv_feature and send_feature only accept 'exact' and 'mask' for now.