DRY fetch of msglists.

DRY fetch of msglists.

A lot of the calls to cdb_fetch(CDB_MSGLISTS...) follow the same design pattern
and many of them are in need of rework to handle how they free their memory.  So
I created a new function CtdlGetMsgList() to do it in a consistent way.  Three
callers have been migrated to the new syntax.