Proposal: Extensible exceptions

[Yitzchak Gale]

Hi Bulat,

I wrote:
>> o For 6.10, make the new Exceptions available so that
>>   everyone can start working on switching, but leave old
>>   Exceptions as the default so that existing programs still
>>   work. Prominently mark old exceptions as deprecated
>>   in all documentation.
>
>> o In the next version, make the new Exceptions the default.
>>   Make sure that programs using new Exceptions for 6.10
>>   will still work (e.g., leave NewException as an alias for
>>   Exception, or whatever).

Bulat Ziganshin wrote:
> oh... all that we need to do is just to use new module name for new
> exceptions

Yes, that would be even better. There seems to be an
assumption that the module name will remain the same,
so that is why I suggested the above.

Regards,
Yitz