[tz] Why did you rename Russian zone name abbreviations

[Paul Eggert]

Sergei Turchanov wrote:
> Why did you rename Russian zone name abbreviations? Can you provide a
> rationale for this change?

Sure, the basic idea is that the tz database should reflect common practice in 
English-language abbreviations, rather than inventing and/or imposing 
abbreviations. So I have been gradually removing invented abbreviations and 
replacing them with UT offsets. I think Russia is mostly done now, and it's time 
to turn our attention to other parts of the world.

> This change breaks date parsing, etc...

Alphabetic zone abbreviations are ambiguous in practice and any date parsing 
depending on them is questionable anyway.

The above is documented in more detail in the 'Theory' file.