QGraphicsAnchorLayout: Fix sequential anchor distribution w/ expanding sizes
QGraphicsAnchorLayout: Fix sequential anchor distribution w/ expanding sizes

After the addition of expanding SizePolicy, the distribution of sequential
anchors became wrong.

We must now account for three intervals of distribution instead of only two.
This commit also unifies the logic used by the sequential group anchor and
the edge interpolator.

Signed-off-by: Eduardo M. Fleury <54231285b1a7e6820e014049a5428d7993c4be1a@openbossa.org>
Reviewed-by: Caio Marcelo de Oliveira Filho <816df4d2f7553426878b7da6111c247d38d5602a@openbossa.org>

radekp/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,radekp/qt,radekp/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,radekp/qt,radekp/qt,igor-sfdc/qt-wk,radekp/qt,radekp/qt