hstore-new - hstore-new: revisit previous fix; unconditionally set

Log Message:
-----------
revisit previous fix; unconditionally set result varlena length in code paths
that otherwise leave content unchanged. Add regression tests accordingly.

Modified Files:
--------------
hstore-new:
hstore.h (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/hstore-new/hstore-new/hstore.h?r1=1.2&r2=1.3)
hstore_op.c (r1.4 -> r1.5)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/hstore-new/hstore-new/hstore_op.c?r1=1.4&r2=1.5)
hstore-new/expected:
hstore.out (r1.4 -> r1.5)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/hstore-new/hstore-new/expected/hstore.out?r1=1.4&r2=1.5)
hstore-new/sql:
hstore.sql (r1.4 -> r1.5)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/hstore-new/hstore-new/sql/hstore.sql?r1=1.4&r2=1.5)