pgsql: Modify pg_upgrade to set/restore all environment variables

Log Message:
-----------
Modify pg_upgrade to set/restore all environment variables related to
collation/encoding to match English when reading controldata.  This now
matches the English variable setting used by pg_regress.c.

Backpatch to 9.0.X.

Modified Files:
--------------
    pgsql/contrib/pg_upgrade:
        controldata.c (r1.9 -> r1.10)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_upgrade/controldata.c?r1=1.9&r2=1.10)
    pgsql/src/port:
        unsetenv.c (r1.11 -> r1.12)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/unsetenv.c?r1=1.11&r2=1.12)