Introduce --no-superuser-check option.

The current client checks for superuser before attempting to
execute pg_repack commands. In Amazon RDS, customers are given
access to a psuedo-superuser role called rds_superuser, but they
are not given access to superuser. However, rds_superusers will
otherwise have the ability to execute pg_repack commands in RDS.

This change introduces the --no-superuser-check option in the
client code so that users can disable the client-side superuser
checks.

doc/pg_repack.rst

@@ -128,6 +128,7 @@ Options:
   -x, --only-indexes        move only indexes of the specified table
   -T, --wait-timeout=SECS   timeout to cancel other backends on conflict
   -Z, --no-analyze          don't analyze at end
+  -k, --no-superuser-check  skip superuser checks in client
 
 Connection options:
   -d, --dbname=DBNAME       database to connect
@@ -210,6 +211,10 @@ Reorg Options
     Disable ANALYZE after a full-table reorganization. If not specified, run
     ANALYZE after the reorganization.
 
+``-k``, ``--no-superuser-check``
+    Skip the superuser checks in the client.  This setting is useful for using
+    pg_repack on platforms that support running it as non-superusers.
+
 
 Connection Options
 ^^^^^^^^^^^^^^^^^^