Merge r263232 from head to stable/10:

Merge r263232 from head to stable/10:

  Rename capability.h to capsicum.h: the original name conflicts with the
  draft POSIX.1e capability.h used on some systems (e.g., Linux).  On
  FreeBSD, leave a wrapper header so that current code continues to compile.

  We will eventually want to deprecate the old header as the presence of a
  capability.h may be confusing some configure scripts.

  Suggested by:   David Drysdale <drysdale at google.com>
  Discussed on:   cl-capsicum-discuss
  MFC after:      3 weeks

Sponsored by:	Google, Inc.

git-svn-id: svn://svn.freebsd.org/base/stable/10@280224 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f