Graphic quality of stamped sprites is very low

[jwzimmer-zz]

From internal playtest, 3/3/17.

Expected Behavior

The stamped sprites shouldn't be appreciably lower-res than the original sprite.

Actual Behavior

The graphic quality of the stamped sprites is really low.

Operating System and Browser

e.g. Mac, Chrome

[thisandagain]

Moved to scratchfoundation/scratch-render#124