Fixed: broken corners on primary CPBox in Chrome.

In Chrome, a primary CPBox (showing the new recessed rounded corner look) had distorted and jagged edges in Chrome due to the clipping mask.

This fix places the clipping mask on integer coordinates which seems to resolve the problem.
_CPJavaScriptArray -objectsAtIndexes: implementation.
Added speed test in CPArrayPerformanceTest (6x faster).
Fixed: in recent CPBox versions, corner radius set in IB was ignored.

Without this fix, setting a corner radius of 0 on a CPBoxCustom resulted in there being a corner radius anyhow.

This fix makes sure to preserve the corner radius, border width and margins for non-primary style boxes.
Fixed: CPBox with CPBezelBorder had unexpected inner shadow.

Without this fix, a CPBoxOldStyle box with a CPBezelBorder would draw with the correct border colour and fill, but with an additional inner shadow, unlike Cocoa.

This fix makes it so that only primary and secondary boxes draw with the special "well"-like shadow style.
Merge pull request #1736 from cacaodev/_CPJavaScriptArray-objectsAtIndexes

_CPJavaScriptArray -objectsAtIndexes: implementation.