parse_map_flags() silently truncates map flags after the first 't' or
'r'. This makes it accept arguments "true" and "revert". However, it
also breaks the perfectly sensible argument "ts", which should show
ships just like "st", but doesn't.
info bmap & friends document arguments "true" and "revert", and also
suggest flags 't' and 'r'. What a mess.
Make argument "revert" a special case. Deprecate flag 'r', and clean
up truncation there.
Don't truncate after flag 't'. If any bad flags follow, ignore
everything after 't', but deprecate that usage.