Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Always assign WARNS using ?=

- fix some nearby style bugs
- include Makefile.inc where it makes sense and reduces duplication

Approved by: ed (co-mentor)

Add basic simplified HTTP benchmark tools to the netrate suite:

- http is a lightweight, multithreaded HTTP query tool, which performs
a timed measurement of the rate at which it can download files using
single-fetch HTTP/1.0. Other than specifying the IP and a URL path,
it requires zero configuration.

- httpd is a lightweight, multithreaded HTTP server tool, which exports
a single file of choice to the HTTP client, and responds with it no
matter what the request. Other than specifying the file to export,
it requires zero configuration.

The goal of these tools is to measure the network costs associated with
HTTP serving, rather than file system, HTTP protocol parsing, error
handling, etc, and as such, parts relating to less interesting components
of HTTP testing are intentionally omitted. Both are linked against
libpthread by default.