bug#9006: 24.0.50; Abort in unshow_buffer/kill-buffer

[martin rudalics]

> This time I wasn't editing but just moving around the buffer rapidly,
> holding down keys like C-n, C-p, C-f, C-v etc. until Emacs didn't
> respond anymore, then C-g, upon which Emacs aborted.  The session was
> not quite as old as the previous one, 9-10 hours.  I had tried
> unsuccessfully to induce the crash several times earlier in the session.

I'm quite lost here.  From the code it seems obvious that tabbar uses
`vertical-motion' which makes a temporary buffer appear in the selected
window without displaying it in order to calculate the tabs to display.
Apparently, the problem is that `vertical-motion' does

      XSETBUFFER (w->buffer, current_buffer);

but does not

      set_marker_both (w->pointm, buffer, BEG, BEG_BYTE);

as the comment I posted earlier suggests.  This makes the subsequent
unshow_buffer abort.  In any case, someone who knows `vertical-motion'
better than me will have to look into this.

martin