Make the locale comparison in pg_upgrade more lenient

If the locale names are not equal, try to canonicalize both of them by
passing them to setlocale(). Before, we only canonicalized the old cluster's
locale if upgrading from a 8.4-9.2 server, but we also need to canonicalize
when upgrading from a pre-8.4 server. That was an oversight in the code. But
we should also canonicalize on newer server versions, so that we cope if the
canonical form changes from one release to another. I'm about to do just
that to fix bug #11431, by mapping a locale name that contains non-ASCII
characters to a pure-ASCII alias of the same locale.

This is partial backpatch of commit 33755e8edf149dabfc0ed9b697a84f70b0cca0de
in master. Apply to 9.2, 9.3 and 9.4. The canonicalization code didn't exist
before 9.2. In 9.2 and 9.3, this effectively also back-patches the changes
from commit 58274728fb8e087049df67c0eee903d9743fdeda, to be more lax about
the spelling of the encoding in the locale names.
Work around Windows locale name with non-ASCII character.

Windows has one a locale whose name contains a non-ASCII character:
"Norwegian (Bokmål)" (that's an 'a' with a ring on top). That causes
trouble; when passing it setlocale(), it's not clear what encoding the
argument should be in. Another problem is that the locale name is stored in
pg_database catalog table, and the encoding used there depends on what
server encoding happens to be in use when the database is created. For
example, if you issue the CREATE DATABASE when connected to a UTF-8
database, the locale name is stored in pg_database in UTF-8. As long as all
locale names are pure ASCII, that's not a problem.

To work around that, map the troublesome locale name to a pure-ASCII alias
of the same locale, "norwegian-bokmal".

Now, this doesn't change the existing values that are already in
pg_database and in postgresql.conf. Old clusters will need to be fixed
manually. Instructions for that need to be put in the release notes.

This fixes bug #11431 reported by Alon Siman-Tov. Backpatch to 9.2;
backpatching further would require more work than seems worth it.