Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Fix a typo in the upgrade directions

MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division

The ATF source code is now hosted on GitHub.

Update notes for imports of atf.

This is because the atf vendor branch now includes a verbatim copy of
the distfile sources. As a result, the list of files to-be-removed from
the contrib/ directory is now more aggressive (and different) and the
upgrade notes now only describe stuff that is specific to the atf import
and is not documented in the Subversion Primer.

Approved by: rpaulo (mentor)

Add ATF update instructions and file exclude list.

Submitted by: Garrett Cooper <yanegomi@gmail.com>