mrpdclient: mrpdclient_close() send a "BYE" before closing connection

The "BYE" message allows the mrpd daemon to free a client connection.
This commit thus prevent a leak risk by both sending this message and
closing the socket on client side.
mrpl, mrpq: free mrpd daemon message buffer

Bug introduced by previous commit.
mrpl: mrpdclient_sendto does not return 0/-1, so don't OR its return
Merge pull request #164 from jbmaillet/mrpdclient_close_says_BYE

mrpdclient: mrpdclient_close() send a "BYE" before closing connection