Force Amazon AC requests to use 10-digit ISBNs

Force Amazon AC requests to use 10-digit ISBNs

Inspired by a patch submitted by Ian Bays <ian.bays@ptfs-europe.com>
via https://bugs.launchpad.net/evergreen/+bug/870171, this patch takes
the incoming key and, if it is longer than 10 characters (a 10-digit
ISBN or Amazon ID), attempts to normalize it and return a 10-digit ISBN.

We don't normalize all incoming keys because some sites are horribly
abusing the 020 MARC field to include an Amazon ID instead of an ISBN -
but that works in practice and we'd rather not break working
installations if we can avoid it.

Signed-off-by: Dan Scott <dscott@laurentian.ca>