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.

Tags:
----
REL9_0_STABLE

Modified Files:
--------------
pgsql/contrib/pg_upgrade:
controldata.c (r1.9 -> r1.9.2.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_upgrade/controldata.c?r1=1.9&r2=1.9.2.1)
pgsql/src/port:
unsetenv.c (r1.11 -> r1.11.6.1)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/unsetenv.c?r1=1.11&r2=1.11.6.1)