Re: [PATCH v2] whitespace: correct bit assignment comments

> A comment in diff.c claimed that bits up to 12th (counting from 0th)
> are whitespace rules, and 13th thru 15th are for new/old/context,
> but it turns out it was miscounting.  Correct them, and clarify
> where the whitespace rule bits come from in the comment.  Extend bit
> assignment comments to cover bits used for color-moved, which
> weren't described.
> 
> Also update the way these bit constants are defined to use (1 << N)
> notation, instead of octal constants, as it tends to make it easier
> to notice a breakage like this.
> 
> Sprinkle a few blank lines between logically distinct groups of CPP
> macro definitions to make them easier to read.