Test layout engine fundamentals

Done with Jan Arve

Task-number: QTBUG-33104

Change-Id: I8319748536d448d1c37a26527ced53156d8c2f56
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Don't compare const_iterator with iterator.

Commit 93ffb81df6e2cdc57ac8f70c6578f132024d7117 introduced this bug. As
it is in the header, it affects downstreams.

Change-Id: I02e86927e648153ca7c0b66ac945a7f99cc4cd89
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>