Error from equality check are swallowed when filtering for trait change events

The existing behaviour for `on_trait_change` (and `observe`) is that if equality check fails, the error will be swallowed and the change handler is fired. This issue is about whether we should do something else with the exception instead of or in addition to swallowing it.

Currently the relevant code is here, but that is being moved by #1165:
https://github.com/enthought/traits/blob/aa6353148570cf4aa49144d7e147529874a3e2d6/traits/ctraits.c#L2366-L2370

Here is the existing behaviour (nothing fails, and nothing is logged):
```
from traits.api import *

class NotComparable:

def __eq__(self):
raise RuntimeError("Sorry!")

class Foo(HasTraits):
dummy = Any()

def handler(_):
print("changed")

foo = Foo()
foo.on_trait_change(handler, "dummy")
foo.dummy = NotComparable() # print 'changed'
foo.dummy = NotComparable() # print 'changed'

foo = Foo()
foo.observe(handler, "dummy")
foo.dummy = NotComparable() # print 'changed'
foo.dummy = NotComparable() # print 'changed'
```