Rewrite of IBM doublebyte charsets

[Xueming Shen]

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

Sherman