checkpolicy: new package

[Thomas:
 - Indicate in the Config.in help text that this policy compiler is
   SELinux related.
 - Rewrap Config.in help text and remove trailing white space.
 - Add a comment in the .mk file to indicate why we're passing
   DESTDIR= at build time.]

Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Clayton Shotwell <clshotwe@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>