MFC r282072,r283018:

r282072:

- Fix compilation (MAP_INHERIT's dead)
- Fix warnings
- Use mkstemp instead of tmpnam

r283018:

Fix more warnings related to missing headers

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

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

Usage style sweep: spell "usage" with a small 'u'.
Also change one case of blatant __progname abuse (several more remain)
This commit does not touch anything in src/{contrib,crypto,gnu}/.

These are regression tests for the P1003.1B scheduler.

Approved by: jkh