Improve updatability checking for views and foreign tables.

Extend the FDW API (which we already changed for 9.3) so that an FDW can
report whether specific foreign tables are insertable/updatable/deletable.
The default assumption continues to be that they're updatable if the
relevant executor callback function is supplied by the FDW, but finer
granularity is now possible.  As a test case, add an "updatable" option to
contrib/postgres_fdw.

This patch also fixes the information_schema views, which previously did
not think that foreign tables were ever updatable, and fixes
view_is_auto_updatable() so that a view on a foreign table can be
auto-updatable.

initdb forced due to changes in information_schema views and the functions
they rely on.  This is a bit unfortunate to do post-beta1, but if we don't
change this now then we'll have another API break for FDWs when we do
change it.

Dean Rasheed, somewhat editorialized on by Tom Lane

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -88,6 +88,7 @@ ALTER FOREIGN TABLE ft2 DROP COLUMN cx;
 -- configure options
 ALTER SERVER testserver1 OPTIONS (
 	use_remote_estimate 'false',
+	updatable 'true',
 	fdw_startup_cost '123.456',
 	fdw_tuple_cost '0.123',
 	service 'value',