Fix race condition when switching tabs fast

Since changeset 894fb914ef79, the set_cursor on form doesn't detect it was
closed and so the cursor widget is no more there.

review3401002
Missing removal of early attribute clearing in destroy

This one was missing in changeset 894fb914ef79

review3441002
Fix domain inversion for xxx2many fields

issue3659
review3311002
Allow to close wizard if end state transition exists

issue3652
review3291002
Remove unused view cancel