Add specs for http range header.

According to
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35.1
Fix host negotiation

This reintroduces the "host" to "request.terms" if a host is
successfully negotiated, to notify downstream apps of which host pattern
matched.
Fix range content HTTP requests

Further work needed to be fully conformant, particularly for multiple,
non-contiguous range requests; and multiple, mixed-validity range
requests.
Merge pull request #79 from kriskowal/range-fix

Range fix