Newly posted replies (by the current user) did not appear in the message list.
The message list was never re-loaded: I added a Ctrl-R command key to reload
the message list manually and it's also automatically reloaded when replying
via a public-posted message (email replies don't force a reload).

The sub-board's last-read pointer is also updated whenever the current msg
selection is moved, even if the message isn't read or previewed. This paves
the way for the internal message reader to possibly track to the current
message selected in the msglist module upon exit.

Included in here is a work-around for the (just-fixed) MsgBase.get_index/
get_all_msg_headers() bug where the msgbase status header was not re-read
before determining the max number of messages to load. That work-around will
be removed eventually.