BRect to clipping_rect with simple C casts. I think this
is more adequate, since clipping_rects are used for
pixel indices. This change fixes some graphics problems too,
it appears that cursor coords are fractional on Haiku, even
with a normal mouse. In Playground, this resulted in the
hit points being rendered wrongly.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@16840 a95241bf-73f2-0310-859d-f6bbb57e9c96