Message3879

We should utilize the nio charsets for these. One gotcha is they encode 
to/decode from actual bytes, not chars (as they should) -- and of course 
our byte bucket (str) is based on chars.

In that case we could probably make the streaming from/to our 'byte 
bucket' more efficient by faking a ByteBuffer that gave back bytes 
from/put back bytes to an underlying char array. That'd avoid an extra 
conversion pass.

The Encoder/Decoder implementations seem to go through the actual 
ByteBuffer methods -- i.e. not through the underlying Buffer arrays 
directly. That'd allow this hack

A CharsetDecoder can take a ByteBuffer instance to fill into -- we'd 
have to use that for this hack, since Charset.encode returns an entirely 
new ByteBuffer

This hack would be kind of a lame, but would go away in Jython 3. Or we 
could just do the extra pass

Another gotcha would be -- can we still retain our error handling 
behavior with Java's Charsets? Briefly looking at them, they seem to 
have fairly similar error handling facilities