_solve_..slot_conflicts: fix bug #522084

Fix _solve_non_slot_operator_slot_conflicts to add all parents to the
conflict_graph, even for parents where the atom matches all relevant
nodes. Otherwise, we risk removing all of the matched nodes from the
graph, which would cause a missed update.

X-Gentoo-Bug: 522084
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=522084
Reviewed-by: Alexander Berntsen <bernalex@gentoo.org>
_quickpkg_dblink: fix bug #523152

This fixes the unmerge-backup and downgrade-backup features to be
compatible with the new setup.py quickpkg install location, while
preserving compatibility for running from a source tree (for unit tests
or development purposes). If not running from a source tree, then the
PATH variable is used to locate the quickpkg binary.

X-Gentoo-Bug: 523152
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=523152