Make InstantClick work on more sites without configuration

The goal of these changes is to make IC work on more sites without requiring the addition of `data-` attribute configuration.  Before these changes, it was common for sites which had changes in their head to break after IC navigation.  I tried to make the commit messages descriptive, so please consult them for a specific list of the changes required.

Here's a few examples of sites broken w/ master which now work:

- dropbox.com – Click “Mobile” in the footer
- mit.edu – Click “About” or “Visiting"
- twitter.com/privacy – Click “About Us” in the footer
- nytimes.com – Click “Opinion” in the top nav, or worse, click an article title
- apple.com – Click “iPhone"
- github.hubspot.com/offline/docs/welcome – Click “Documentation”

The one note about these changes is they don't target Firefox before version 13.  This amounts to about 0.2% of the web browser market.  If this is an issue, let me know and I will tweak the solutions to work on those older browsers as well.