Missing ST_IsValid for Geography Types

[rfcmedia]

There is no ST_IsValid for geography types.

I do not think casting a geography as a geometry and then running it through ST_IsValid will yield correct results either.

Consider a polygon (-170 0, 170 0, 178 5, 178 -5, -170 0) in degrees on a spherical surface. This is not a valid polygon as there is clearly an intersection between two lines at (178, 0) but this would be considered a valid polygon if it were cast as a geometry.

[mwtoews]

It would also be valuable to have a regression table to evaluate what is valid or invalid, similar to: http://trac.osgeo.org/postgis/browser/trunk/regress/isvalid_test

[strk]

This one doesn't sounds likely to happen for 2.0, correct me if I'm wrong.