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.

doc/src/sgml/plperl.sgml

@@ -125,6 +125,14 @@ $$ LANGUAGE plperl;
 </programlisting>
   </para>
 
+  <note>
+    <para>
+      Arguments will be converted from the database's encoding to UTF-8 
+      for use inside plperl, and then converted from UTF-8 back to the 
+      database encoding upon return. 
+    </para>
+  </note>
+
   <para>
    If an SQL null value<indexterm><primary>null value</><secondary
    sortas="PL/Perl">in PL/Perl</></indexterm> is passed to a function,