wish: address "waiting queries" through code or docs

[markstos]

I've used an old alternate monitoring plugin called "check_pg_waiting_queries.pl". It's poorly written, so that when it's run against PostgreSQL 9.1, it always reports "success" when in fact the query contains a syntax error, so it should fail.

I presume that check_postgres.pl provides an appropriate upgrade path, or that I don't actually need this monitor at all, but I'm not quite clear. I see that check_postgres.pl provides a check for locks, and I know that locks are closely related to "waiting queries". If the "locks" check is an appropriate replacement for a "waiting queries" check, it would be helpful if a sentence could be added to those docs to clarify it.