1. fixed many warnings about implicit double to int conversions in newly

1. fixed many warnings about implicit double to int conversions in newly
   checked in "advanced" image manipulation stuff
   (could we please avoid checking in the code with warnings?)
2. tried to simplify the new code a little, but much remains to be done,
   in particular it seems obvious that BlurVertical/Horizontal() must be
   refactored to avoid duplicating each other
3. reformatted (avoid jumbo lines, removed unnecessary double casts, declare
   the variables at the point of use, ...)

Hope this didn't break anything but as there are no tests it's really hard to
find out how was this supposed to behave.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41418 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775