ConicalGradient modified to produce sharp gradient edge.
ConicalGradient modified to produce sharp gradient edge.

Previously ConicalGradient produced smooth antialiased transition
between gradient position 1.0 and 0.0. However this suffered
from accuracy problem and transition was spreading more at
pixels that were far away from the gradient center. Thus is is
better to produce sharp consistent transition. Anti-aliased
look can still be achieved by defining the gradient steps and
colors in suitable way near the 1.0 position.

Change-Id: I67040c5c56fdf855fe68d9b3f0d9fde0cc37b59f
Reviewed-by: Kim Gronholm <48e0d40fe5e2fc76008f07e0fdece8a523fc2690@nokia.com>

kobolabs/qtgraphicaleffects