add_pkg_dep_string: respect traverse_ignored_deps

I don't think this makes any difference now, but it clarifies how
traverse_ignored_deps should behave.
(cherry picked from commit af430c8b439cf67079b54fa3b18312e0a6afce8d)
diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index 9811e14..22937aa 100644
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -1565,7 +1565,8 @@
 					self._dynamic_config._ignored_deps.append(dep)
 
 			if not ignored:
-				if dep_priority.ignored:
+				if dep_priority.ignored and \
+					not self._dynamic_config._traverse_ignored_deps:
 					if is_virt and dep.child is not None:
 						traversed_virt_pkgs.add(dep.child)
 					dep.child = None
@@ -1595,7 +1596,8 @@
 					(virt_pkg.cpv, [str(x) for x in atoms]),
 					noiselevel=-1, level=logging.DEBUG)
 
-			if not dep_priority.ignored:
+			if not dep_priority.ignored or \
+				self._dynamic_config._traverse_ignored_deps:
 				if not self._add_pkg(virt_pkg, virt_dep):
 					return 0
 
@@ -1657,7 +1659,8 @@
 						self._dynamic_config._ignored_deps.append(dep)
 
 				if not ignored:
-					if dep_priority.ignored:
+					if dep_priority.ignored and \
+						not self._dynamic_config._traverse_ignored_deps:
 						if is_virt and dep.child is not None:
 							traversed_virt_pkgs.add(dep.child)
 						dep.child = None