- external programs section (default: "xtrn_sec")
- logon list (default: "logonlist")

This ties the Baja XTRN_SECTION and USERLIST_LOGONS functions and the
JS bbs.xtrn_sec() and bbs.list_logons() methods to the loadable modules (if
configured) automatically without the exec_bin hackery in *.src.

Also, allow the xtrn section argument to be passed to the JS/C++ method to
go directly to a specific xtrn program section.

The bbs.list_logons() can also accept an argument to pass to the module
(e.g. "-y" for yesterday's logons).