I noticed that the node status displayed by load/presence_lib.js (e.g. used
by exec/nodelist.js) would have (N) for node-message waiting instead of (M)
as is reported in other places (e.g. the node utility, umonitor, sbbsctrl).
So this commit commonizes this behavior.

Now, it's crazy that there are (at least) 3 places that this node status
display is implemented and more things should just use nodestatus() to get
that string, but I'm not solving that copy/pasta issue in this commit.