Tidy comments
dup/dup2 should preserve rights
Coalesce licensing information & tidy header comments

Create LICENSE file with the master license, which is a BSD 2-clause
license.  Remove individual file license texts.

For the portions of this code that were originally derived
from the previous Capsicum Linux port (marked as (c) Chromium OS
Authors), move from GPLv2 to BSD 2-clause for consistency.
Test various specific fcntl(2) operations