Fixes the table_percentage_width_a.html reftest with incremental reflow turned on.

This also enables incremental reflow by default. \o/

r? @pcwalton
I think what you want to call this is "intrinsic column inline sizes". The comment should say "intrinsic column inline sizes according to INTRINSIC § 4.1".

Also, can you put a FIXME on `column_inline_sizes` that it should be a separate type that only contains computed inline sizes, and change the comment from "inline-size information" to "computed inline-size"? The idea here is to separate out the intrinsic widths, which are computed in bubble-widths, from the computed widths, which are computed during assign-widths.