Add back local package installation support, which was disabled for PKG_NG.
The patch attached to PR 181450 did no longer apply cleanly, therefore I
edited portmaster to follow the intent and in part the letter of the patch.
This patch should not affect port building in any way. I have no use for
the feature (and I'm still considering to completely remove support for the
installation of packages in portmaster), and therefore did not test that
it performs as expected by the submitter.

PR: 181450
Submitted by: rozhuk.im@gmail.com
Approved by: antoine (implicit)