QHeaderView - resizeSection improvement

QHeaderView - resizeSection improvement

This patch improves the manual resizeSection a bit. Before we didn't
consider that the program could maybe resize other sections when the
user was resizing one section.

The main issue with that is that setOffset is so smart that it helps
moving the mouse cursor - however it really shouldn't do if the
program is trying to change something too.

Maybe this won't solve all (possible) problems at once - but it is
a fixed needed just to make something work - trying to make anything
work without this fix is horrible....

Change-Id: I3cefa375a9b8ee4c1ef1e08ba0900025c671e4c6
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>