Shorten: tighten up triggering.

- Only shorten a single remaining "word"
- Require that word to contain a dot (for quad or domain, at least)
- Expand testing to cover more cases

Fixes #1106.
Shorten: allow for some connector words.

Also, hide the fact that I previously committed a broken test.
Merge pull request #1107 from mwmiller/gd_urls

Shorten: tighten up triggering.