MsgBase.save_msg() method. The bug was that it was forcing the idx.to value to
0 which would only work (in theory) for mail going to a QWKnet hub.
Now, save_msg() will check the 'to_net_addr' property of the header object
(or recipient objects) and actually verify that it/they are routeable QWKnet
address(es) and throw an exception if not.
If the first hop is a QWKnet node, sets the to_ext (and thus, idx.to value) to
the account number of the node. This also looks up full-routes via the
route.dat and replaces the to_net_addr value with the full route if necessary.
I guess nobody (including me) tried sending QWKnet netmail via JS before.