Remove utils.intercept; it has performance issues.

This issue arises because v8 does not optimize any function that abuses `arguments`.

Fixes #948.
Version 1.2.3
Move focus() and blur() into HTMLElement proto
Add living-html/focus test for existence of HTMLElement.focus
Uncomment Sizzle focus tests

See https://github.com/jquery/sizzle/issues/163 for the modifications made. We should update Sizzle sometime.