Reorg+add test for #452
Using uint* for pixel access in mode I;16 and I;32, fixes #452
reverted int32 changes
longer benchmark
Raising proper ValueErrors
clamping channels to 255
use cffi by default in pypy, not in c-python
trying to bust up the JIT a bit
LA, PA image modes
I;16 modes
Merge branch 'i16-pixelaccess' into cffi-pixelaccess
detailed tests for I;16 modes, merged from i16-pixelaccess branch