When the QHeaderView model rowCount is decreased then the headerview
needs to remove some sections.
If e.g swapSections had occured then qheaderview before this patch did
a very slow removal by removing one section at a time and for each section
it restored visual and logical indexes.
By temporarily storing the logical index on the section we
can reduce the execution time of this a lot. The old code is only
faster when we remove one index (and is kept for that situation)
There is a complexity in difference (and many factors in our
qheaderview benchmark (the trunc part))
Change-Id: If45eab17fbca3364d458b004980570b5d013e4bd
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
a4e4c31007