Force strings passed to and from plperl to be in UTF8 encoding.

Force strings passed to and from plperl to be in UTF8 encoding.

String are converted to UTF8 on the way into perl and to the
database encoding on the way back. This avoids a number of
observed anomalies, and ensures Perl a consistent view of the
world.

Some minor code cleanups are also accomplished.

Alex Hunsaker, reviewed by Andy Colson.