Add some c3p0 utilities.

- C3P0Propertizer which knows how to turn c3p0 Config into a Properties object that c3p0 will grok.
  Unfortunately this involves sticking a Map into the value of the Property, specifically for the
  "extensions" configuration: http://www.mchange.com/projects/c3p0/#extensions

- ConnectionCustomizer that can be used to run SQL at any of the four stages of connection lifecycle
  that c3p0 exposes.  Beyond me why this isn't already part of c3p0 itself.

This is then going to be used to set postgres parameters such as work_mem on connection acquire.