Fix case insensitive comparisons using QCollator

In ICU the strength parameter decides whether a comparison is
case sensitive or not.

Fix mac comparison code. It can't have worked before.

Added some basic automated testing for QCollator.

Change-Id: I2646c464fd22ccd3a93c461fa3dba4bd1d4c7b4b
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>