This should fix OMP/MT
fix #3513
fix #3505
fix bug in MoveDef::TestMoveSquare
fix some cases of units getting perma-stuck (s.t. even spammed user orders cannot free them) on terrain
fix #3489 (default trees not obeying featureLoS rules)
un-duplicate *TreeDrawer::TreeSquareStruct
fix #3498, unit double click select units of same type in view

I.e. it no longer selects a group if unit is in a group.
QTPFS: fix a large part of #3423
make mutual push-resistant unit collisions more like 0.82.x (smoth's issue)
Merge branch 'release' of github.com:spring/spring into release
Merge branch 'release' into develop