MFC: 234851, 235059

MFC: 234851, 235059

Add two special directives to libmap.conf:
include <file>:
  Parse the contents of file before continuing with the current file.
includedir <dir>:
  Parse the contents of every file in dir that ends in .conf before continuing
  with the current file.
Any file or directory encountered while processing include or includedir
directives will be parsed exactly once, even if it is encountered multiple
times.

Approved by:	des (mentor)

git-svn-id: svn://svn.freebsd.org/base/stable/9@236523 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f