Emoji doesn't render in post titles

[pento]

Chrome 41 added native support for emoji in OS X, it seems that emoji doesn't render in post headings in Twenty Ten, Twenty Eleven, and Twenty Fifteen.

Twenty Twelve, Twenty Thirteen, and Twenty Fourteen render emoji correctly in headings.

[pento]

It turns out that Chrome won't render coloured emoji when the font-weight is greater than 500. We'll need to handle this in WPEmoji, instead.