Add support for the PATCH verb to Pound.

PATCH is another HTTP verb commonly used in modern API frameworks to
indicate a user is making a partial change to a resource. It's now an
option included when you also activate PUT and DELETE.

Import v2.7d from vendor

Import v2.7c from vendor

Import v2.7b from vendor

Import Pound-2.7a.tgz from vendor

Fix missing comma in threadmodel patch

Import Pound 2.6 from vendor

import 2.6f from vendor

import 2.6e from vendor

import 2.6d from vendor