Fix incompatible encodings error in RKellyAdapter.

Convert latin1 escape sequences into UTF-8.  By default they resulted
in ASCII-8BIT (binary) encoding, which wasn't compatible with UTF-8,
resulting in error.

Added wrapper encoding method to cope with Ruby 1.8 which has no
builtin encodings support.

The tests file is now also a pure ASCII file, so no funky encoding-stuff
happens there.

Fixes #491