pgsql: Fix the assert_enabled issue properly.

Log Message:
-----------
Fix the assert_enabled issue properly.  This eliminates the former ABI
difference between USE_ASSERT_CHECKING and not: the assert_enabled
variable is always there.

Modified Files:
--------------
    pgsql/contrib/ltree:
        _ltree_gist.c (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/ltree/_ltree_gist.c.diff?r1=1.14&r2=1.15)
        ltree_gist.c (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/ltree/ltree_gist.c.diff?r1=1.12&r2=1.13)
    pgsql/src/backend/port:
        ipc_test.c (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/port/ipc_test.c.diff?r1=1.18&r2=1.19)
    pgsql/src/backend/utils/misc:
        guc.c (r1.307 -> r1.308)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.307&r2=1.308)
    pgsql/src/include:
        postgres.h (r1.71 -> r1.72)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/postgres.h.diff?r1=1.71&r2=1.72)