Fixes #5808: Handle missing techniques with active techniques in trees
Merge pull request #664 from fanf/bug_5808/manage_missing_techniques_in_trees

Fixes #5808: Handle missing techniques with active techniques in trees
Merge branch 'branches/rudder/2.10' into branches/rudder/2.11
Merge branch 'branches/rudder/2.11' into branches/rudder/3.0