pgsql: Use "upgrade" in preference over "migrate" in pg_upgrade message

Use "upgrade" in preference over "migrate" in pg_upgrade messages and
documentation. (Many were left over from the old pg_migrator naming.)

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=16b5e08decc8207ae35589add387dce9b62669de

Modified Files
--------------
contrib/pg_upgrade/check.c | 10 ++++----
contrib/pg_upgrade/controldata.c | 6 ++--
contrib/pg_upgrade/info.c | 4 +-
contrib/pg_upgrade/option.c | 3 +-
contrib/pg_upgrade/pg_upgrade.c | 4 +-
contrib/pg_upgrade/relfilenode.c | 2 +-
contrib/pg_upgrade/tablespace.c | 2 +-
contrib/pg_upgrade/version.c | 2 +-
contrib/pg_upgrade/version_old_8_3.c | 12 +++++-----
doc/src/sgml/pgupgrade.sgml | 42 +++++++++++++++++-----------------
10 files changed, 43 insertions(+), 44 deletions(-)