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 multi-repository support by properly respecting 'enabled' flag.

This will read the REPOS_DIR env/config setting (default is /etc/pkg
and /usr/local/etc/pkg/repos) and use the last enabled repository.

This can be changed in the environment using a comma-separated list,
or in /usr/local/etc/pkg.conf with JSON array syntax of:
REPOS_DIR: ["/etc/pkg", "/usr/local/etc/pkg/repos"]

Approved by: bapt
MFC after: 1 week

Follow-up to r258227 and document 'enabled' as a boolean instead of
a string.

Approved by: bapt
MFC after: 2 days
X-MFC-With: r258227

Use proper capitalization for FreeBSD.org

Approved by: bapt
MFC after: 2 days

Add -f support to 'pkg bootstrap' and 'pkg add' to force installation
of pkg(8) even if already installed.

This is useful if you somehow messup pkg(8) and need to reinstall from
remote with it already being registered in the pkg(8) /var/db/pkg database.

Also add some sanity checks to 'pkg add'.

Approved by: bapt
MFC after: 2 days

A few minor mdoc improvements.

Add a pkg(7) manpage for bootstrap

Approved by: bapt
MFC after: 2 days