pgsql: Fix output of ISBN-13 numbers beginning with 979.

Fix output of ISBN-13 numbers beginning with 979.

An EAN beginning with 979 (but not 9790 - those are ISMN's) are accepted
as ISBN numbers, but they cannot be represented in the old, 10-digit ISBN
format. They must be output in the new 13-digit ISBN-13 format. We printed
out an incorrect value for those.

Also add a regression test, to test this and some other basic functionality
of the module.

Patch by Fabien Coelho. This fixes bug #13442, reported by B.Z. Backpatch
to 9.1, where we started to recognize ISBN-13 numbers.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/2d19a0e977080713bd7bb370b20a0025fba6c794

Modified Files
--------------
contrib/isn/Makefile | 2 +
contrib/isn/expected/isn.out | 222 ++++++++++++++++++++++++++++++++++++++++++
contrib/isn/isn.c | 27 +++--
contrib/isn/sql/isn.sql | 104 ++++++++++++++++++++
4 files changed, 345 insertions(+), 10 deletions(-)