pgsql: Fix to_char YYY, YY, Y format codes so that FM zero-suppression

Log Message:
-----------
Fix to_char YYY, YY, Y format codes so that FM zero-suppression really works,
rather than only sort-of working as the previous attempt had left it.
Clean up some unnecessary differences between the way these were coded and
the way the YYYY case was coded. Update the regression test cases that
proved that it wasn't working.

Modified Files:
--------------
pgsql/src/backend/utils/adt:
formatting.c (r1.169 -> r1.170)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/formatting.c?r1=1.169&r2=1.170)
pgsql/src/test/regress/expected:
timestamp.out (r1.41 -> r1.42)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamp.out?r1=1.41&r2=1.42)
timestamptz.out (r1.35 -> r1.36)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/timestamptz.out?r1=1.35&r2=1.36)