New subplot position synchronization

[Konstantinos Poulios]

Hi all,

I have just pushed two changesets to the default branch. The first one,
http://hg.savannah.gnu.org/hgweb/octave/rev/abfcb5d5641b
concerns a minor issue with plotyy and it could also go to the stable
branch. I just preferred not to take the risk of pushing anything to
stable.

The second changeset is the important one:
http://hg.savannah.gnu.org/hgweb/octave/rev/5cbf660e649d

- Fixes bug #31610 for the fltk graphics toolkit but not for gnuplot.
- Implements *real* synchronization of subplot positions for the fltk graphics.
- The regression in demo("axis",4) is *not* caused by this changeset.
It just triggers bug #33112. All other test plots seem to work
correctly.

Please report any regressions, so that I can try to fix them.

Concerning the new changelog and branches policies I hope that I did
the commit correctly.

BR

Kostas