PR 18785: alternative patch

[Geoffrey Keating]

I looked at both of these, and realised that I'd do it neither way.

What I'd do is, like Roger, build up a global table (not a 'huge'
table, one that contains 256 1-byte entries) that maps between the
required part of the host and target character sets.  However, like
Zack, I would never have special 'outs' for the case where
host==target; I would always use the table.

... I'm sure you now both want to explain why I'm wrong :-)