bug#16923: 24.3.50; reression: `set-frame-size' loses mode line

[Drew Adams]

> Anyway - the two puzzling aspects are that the mode line apparently gets
> erased (who can do such a thing to the mode line?) while the header line
> remains unharmed.

Wrt the mode line, let me correct something I said earlier.

I thought that the space was there for the mode line, but without
the mode line text, faces, mouseover etc., i.e., as if there were
an extra blank buffer line.  I was wrong about that.

Checking again, I see that the buffer text extends to the bottom frame
border, just as it does when frame parameter `modeline' has value nil.
IOW, the mode line is apparently just not there; it is not just that it
is displayed wrong.  However, `frame-parameters' shows the `mode-line'
parameter value to be `t'.