[IMP] onchange: new onchange API:

All onchanges are now done server side in one call.
This commit only adapt the client js
[IMP] models: make method onchange() compute the fixpoint of onchanges
[FIX] models, test_new_api: adapts tests of onchange(), and fix onchange() to return dirty values only
[IMP] models: in onchange(), process old-style on_change more completely
[FIX] web: set `field_parent` in context when calling `onchange`
[FIX] models: when evaluating old-api onchange, onchange with single parameter was misinterpreted
[IMP] models: refactor calls to onchange and view spec in tests and yaml_import
[IMP] test_new_api: remove unused import
[FIX] models: revert changes in yaml_import, and make _onchange_spec() more robust
Merge pull request #12 from odoo-dev/master-apiculture-onchange

Make method onchange() recursively apply onchange methods (old and new api)