Fixed artifacts when drawing same line with different clips.

Expanding on the change fixing QTBUG-24762 with the realization that any
line needs to be drawn in a consistent way regardless of system or
painter clip, not just dashed lines.

Task-number: QTBUG-25036
Change-Id: Ief7ef19cc92c52e7d792500a581a072ba032767e
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Correct QDate and QTime documentation.

Task-number: QTBUG-30055

Change-Id: I94c8e023f5e3d23ff2f1c74d0763b1c825deb3d1
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>