pgsql: Fix LIKE's special-case code for % followed by _.

Log Message:
-----------
Fix LIKE's special-case code for % followed by _. I'm not entirely sure that
this case is worth a special code path, but a special code path that gets
the boundary condition wrong is definitely no good. Per bug #4821 from
Andrew Gierth.

In passing, clean up some minor code formatting issues (excess parentheses
and blank lines in odd places).

Back-patch to 8.3, where the bug was introduced.

Modified Files:
--------------
pgsql/src/backend/utils/adt:
like_match.c (r1.24 -> r1.25)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/like_match.c?r1=1.24&r2=1.25)
pgsql/src/test/regress/expected:
strings.out (r1.37 -> r1.38)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/strings.out?r1=1.37&r2=1.38)
pgsql/src/test/regress/sql:
strings.sql (r1.25 -> r1.26)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/strings.sql?r1=1.25&r2=1.26)