Log Message:
Readd pkg_comp, now at version 2.0:

**Released on 2017-02-17.**

This is the first release of the pkg_comp project as a standalone
package.  This new release shares no code with previous versions and is
not compatible with them.

The following are the major differences between pkg_comp 2.0 and all
previous releases, which incidentally are the reasons that triggered
this rewrite:

* Support for multiple platforms.

* Use of pbulk to (re)build packages within the sandbox.  This results
  in more reliable incremental builds after pkgsrc updates.

* Support for bootstrap, generating binary kits as part of the builds.

* Better scriptability to allow running from cron(8) trivially.