Rewrite of IBM doublebyte charsets

[Xueming Shen]

Xueming Shen wrote:
> Ulf Zibis wrote:
>> In IBM933.map you state:
>>
>> #    Warning:
>> #    (2) we "should" have an entry
>> #        25  000a
>> #        in IBM933.nr (b->c only tables) as other ebcdic
>> #        mappings do, but the "old" implementation actually
>> #        maps \u000a to 25. Keep it old behavior for now.
>>
>> I think we shouldn't stick on old behaviour here, as there obviously 
>> was an error in old code, but nobody filed a bug until now.
>>
>
> It's a tough call, and I always try to avoid the touch call:-)
>
> I believe this brain-damage 0x15, 0x25 -> 000a -> 0x15, 0085->0x15 
> mapping is the result of the
> "fix" we made for #4159519, as the workaround solution for the "what 
> is the real new line on ebcdic
> system" problem, while none of the official ebcdic<->unicode mapping 
> tables from IBM/MSFT do
> NOT have this hack documented/recorded at all. So we might want to 
> re-check the soundness of
I meant to say
"none of the official ebcdic<->unicode mapping tables from IBM/MSFT has 
this hack documented/recorded"


> this fix, which was made 10 years ago, sometime.
>
> Sherman
>