need a method to deal with rendering deltas between machines/screens

[zacfilan]

taking a large suite of tests that run on machine one, when moved over to machine have occasional stray pixels on some steps having to do with anti aliasing.

• this can be dealt with s-l-o-w-l-y with existing function, dealing with each delta separately by marking unpredictable or correct. but this sucks for tests with 100s of steps.

• the right answer would be to "turn down" the precision of the antialiaser.

• other options are mark once and persist to all screens forever. in other words these changes apply to every screen, but i only add them once

• another option is "learn mode" play and always push actual into expected.

• another option is to consider a small number of different pixels a pass.

this last one is the easiest to implement.

[zacfilan]

fixed in #71eed1429d9c380cdb044fc9ec8b4d3c7ab609fb by allowing a small number of bad pixels as a pass