Fix various broken things in getting TTLs from response headers.
Use default ttl if Expires: is mangled, not 0.
On second thought, revert that -- using current time is correct.
Adjust tests to accommodate new min_ttl option.
Documentation about testing
Switching now to utcnow
Merge pull request #6 from seomoz/ttl-fix

Various TTL fixes
Merge pull request #2 from seomoz/master

latest from upstream