Obtain terminal type (RFC 1091)

Obtain terminal type (RFC 1091)

Implement rudimentary support for determining the terminal type
reported by RFC 1091 TTYPE compatible clients, and store any initial
value returned in the User.ttype attribute. This implementation does
not iterate over SEND TTYPE commands until UNKNOWN is returned, it
only takes the first value returned and assumes this is the default
terminal type for the user's current connection.