The ir.ui.view.graph_get() method depended on the natural
semi-random order of Python dict keys in the _columns dict.
When the number and/or names of the _columns happened to
yield the o2m field of the "incoming transitions" *before*
the "outgoing transitions" of the "Node model"
(e.g. workflow activity), it would swap the incoming and
outgoing transitions fields around, causing a crash later
in the `tools.graph.process` method (currently an infinite
loop in the `tree_order()` method of tools.graph.py).
Closes#3614
Fixes https://bugs.launchpad.net/openobject-server/+bug/1316948
opw-633765