Update cursor position when selection is reversed.

Update cursor position when selection is reversed.

A reversed selection will have the same resolved start and end
positions but a different cursor position so testing the end points
alone doesn't guarantee the selection is the same.

Task-number: QTBUG-19456
Reviewed-by: Martin Jones
Change-Id: I516e5a501ec878d673f21e54d688fd2d21b624ef
Reviewed-on: http://codereview.qt.nokia.com/2080
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Andrew den Exter <andrew.den-exter@nokia.com>