Fix task failure when loading wikipedia.

There is still an issue with alpha display, so there is
likely a problem elsewhere, but this at least allows the
page to load for now (ref #2554).
Add support for borders on inline elements.

Fix ahem reftests on mac, by disabling text AA in reftest mode.

Also fix precision issues in font metrics to correct height
and baseline calculations.
Merge pull request #3195 from glennw/image-format

Fix task failure when loading wikipedia.
Make some of Node's members private.
Merge pull request #3182 from glennw/inline-text-border

Add support for borders on inline elements
Merge pull request #3202 from Ms2ger/node-priv-members

Make some of Node's members private; r=Manishearth