Working allow_create support in transaction dialogs.
Working allow_create support in transaction dialogs.

Add schevogtk2.form.ExtentChoiceBox and .ExtentChoiceWindow for
selecting an extent when there is more than one allowed extent
for an entity field that has allow_create=True

schevogtk2.form.get_dialog now attaches create-clicked handlers for
each field.

Schevo/schevogtk