hstore-new - hstore-new: fix leakage of wasted space on concatenation

Log Message:
-----------
fix leakage of wasted space on concatenation (bug inherited from old hstore
code). Add regression tests to check data size output from everything that
returns an hstore.

(The bug would cause assert failures or incorrect hash values from hstore_hash)

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