Changelog: add entry for QTBUG-29759

Conflicts:

	dist/changes-5.0.2

Change-Id: Ibdb85dd908368f15530db31b47c901d952bb6d93
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
Boxes: Check for opengl version in .pro file

Make sure that people get an understandable error message when
trying to compile the boxes demo with e.g. ANGLE.

Task-number: QTBUG-30406
Change-Id: I0ba0e26e424d768f95d7977862d9f2c4e85b41fb
Reviewed-by: Jonathan Liu <net147@gmail.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>