Re: monitoring CREATE INDEX [CONCURRENTLY]

For discussion, here's an preliminary patch.  This is just a first
skeleton; needs to grow a lot of flesh yet, per my previous proposal.
As far as the generic CREATE INDEX stuff goes, I think this is complete;
it's missing the AM-specific bits.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services