record the IPs we see
When we found an IP for the hostname in the URL, explicitely use it when making requests.

This way, whe know specifically which IP we are connecting to for the mirror.
Merge pull request #46 from gozer/explicit-ip

Explicit ip
report the X-Cache header, if any, about cache hit/miss
Merge pull request #48 from gozer/cache-info

report the X-Cache header, if any, about cache hit/miss
merge fix