It's unclear whether trailing whitespace is supposed to be significant or not
(FidoNet specs don't say), but I don't see any reason why "John Doe" and
"John Doe " should be considered unique senders or recipients. Remove any
trailing whitespace from message subjects too.

This change makes the trailing whitespace truncation in SMB hash functions
unnecessary (at least for SBBSecho-imported messages), but most (all?) other
message transports don't allow for this nonsense in the first place.