layout: Translate floats when clearing non-floated blocks.

Improves CNN layout considerably.

Closes #3439.
Merge pull request #3454 from pcwalton/float-clear-bug

layout: Translate floats when clearing non-floated blocks.
layout: Adjust the position of block formatting contexts based on float
placement.

Improves Reddit considerably.

Closes #3456.
Merge pull request #3457 from pcwalton/block-formatting-contexts

layout: Adjust the position of block formatting contexts based on float placement.