Emacs mode: push/pop next patch, not patch at point

Emacs mode: push/pop next patch, not patch at point

The three operations we should have are:

  * Pop the topmost applied patch, no matter where point is.

  * Push the first unapplied patch, no matter where point is.

  * Push/pop the patch at point, depending on whether it's currently
    applied.

This patch makes "<" and ">" do the first two operations. The third is
coming in a later patch.

Signed-off-by: Karl Hasselström <kha@treskal.com>
Signed-off-by: David Kågedal <davidk@lysator.liu.se>