Multibyte support revisited

Over the past months I've been refactoring ActiveSupport::Multibyte
and made it run on Ruby 1.8.7 and 1.9. If anyone is interested in a
write-up about the API changes, please let me know.

I've posted the changes as a patch to ticket #951:

You can also pull the changes directly from the multibyte-revisited


p.s. I hope you're not getting this multiple times. It seems Google
Groups is acting up.