Event notification on Enum change with values traits

When using an Enum trait with the values= attribute, it appears that no event notification is sent when the Enum value changes as a result of the values trait changing.

E.g.

``` python
import traits.api as tr
class T(tr.HasTraits):
values=tr.List
enum=tr.Enum(values='values')
@tr.on_trait_change('enum')
def dynamic_event(self):
print 'dynamic event'
def _enum_changed(self):
print 'static event'

t=T()
# values=[],enum=None
t.values=[1,2,3]
# no notification even though enum changed to 1
print t.values, t.enum
t.values=[2,3]
# no notification even though enum changed to 2
print t.values, t.enum
t.enum=3
# now you see both notifications on dynamic/static
```

Start with the provided Python reproduction, focusing on the Enum trait's values= relationship and the notification entry points enum, values, and on_trait_change. Trace how changing values updates enum, then verify that both dynamic and static notifications occur for each resulting enum change.

Written by the indexing model from the issue text.