Exceptionally laconic method to add "SELECT MAX(field) ..." (see below)

Not currently supported with GROUP BY.  Just a single field can be MAXed currently.  Very hackish, but that's by design.

I'm not sure how I feel about having a Command type dedicated to a subset of SELECTs with a particular function, but I don't think it's Wrong (c) 2014.

May want to be more lenient about how you sniff MAX() calls in the future.  Right now, only statements starting with "SELECT MAX(" will trip the SelectMaxCommand.