for writing lastlog to file, -window <ref#|name> for specifying which
window's lastlog to print (output is always to active window) and
-clear option to remove all lastlog lines from window.
git-svn-id: http://svn.irssi.org/repos/irssi/trunk@1255 dbcabf3a-b0e7-0310-adc4-f8d773084564
