[tz] Recent conversions of zones to aliases

[Paul Eggert]

Stephen Colebourne wrote:
> the assumption that IDs would continue to exist
> and not be converted to aliases.

I'm afraid that assumption has been incorrect for the tz database for many 
years, and there's no end-user reason to impose it as a requirement now.

> Jamaica made no difference, and in fact most tzdb changes would not.

I don't expect anybody (other than us time zone nerds) will care about the 
upcoming changes in Indochina either.  The most recent time stamps affected will 
be circa 1975.