Scalepixels: new IOP

Needed to fix NIKON D1X non-square pixels madness
Scalepixels IOP: OpenCL
iop_dependencies.py: add scalepixels
Run iop_dependencies.py after merge!
Flip IOP: modify_roi_in(): drop sanity check

Causes garbage when used with scalepixels.
If it is really needed, it should be rewriten in a way, that has no side-effects like that.