Add tgconstrrelid to stored Trigger structures, make RI trigger functions

Add tgconstrrelid to stored Trigger structures, make RI trigger functions
depend on this rather than the trigger argument strings to locate the
other relation to test.  This makes RI triggers function properly in
the presence of schemas and temp tables.  Along the way, fix bogus lack
of locking in RI triggers, handle quoting of names fully correctly,
compute required sizes of query buffers with some semblance of accuracy.