Fix for #4832 -- Making PSON handle arbitrary binary data

The PSON library needlessly assumed that the data to be transmitted was well-
formed unicode. This made Latin-1 users (and anyone who needed to serialize
arbitrary binary data) sad. This patch goes some of the way to resolving the
issues, by passing through non-unicode data rather than just failing, adds
tests, and cleans up a pernicious assumption about escape characters in ruby
regular expressions not marked "n" (no-encoding).