[mapserver-dev] Implement msPostgisLayerGetExtent

[thomas bonfort]

> As far as I can see in the discussion, a global setting to disable the
> driver extent calculation for the GetCapabilities request would be a good
> consensus, isn't it?

My opinion is that this would be a bare minimum. The difficult
question is whether the expensive extent calculation should set to on
or off by default:
- ON by default: people who have not updated their mapfiles, or people
who do not explicitly disable, are faced with potential denial of
service if they have layers with many features
- OFF by default: the wrong extent calculation continues to cause
unexpected behaviour that isn't trivial to debug

--
thomas