[Python] Raise proper error if custom serialization handler fails

[asfimport]

At the moment, the following fails:

def test_serializaton_callback_error():

    class TempClass(object):
            pass

    # Have a SerializationContext but TempClass is not
    # registered

    serialization_context = pa.SerializationContext()

    with pytest.raises(pa.SerializationCallbackError):
        serialized_object = pa.serialize(TempClass, serialization_context)

This is because serialize will raise a generic ArrowException instead of a SerializationCallbackError. We do need the latter because it contains the object that couldn't be serialized, which is important to give good error messages; in the case of Ray we sometimes want use the object to register additional serialization callbacks on the fly to make the user experience smoother.

Reporter: Philipp Moritz / @pcmoritz
Assignee: Philipp Moritz / @pcmoritz

_{Note: This issue was originally created as ARROW-1450. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1029
#1029