Fix regression test differences between different platforms in the AsGeoJSON regressi...

Fix regression test differences between different platforms in the AsGeoJSON regression code. There were two issues: firstly, the original regression tests included precision information > 15 significant figures, and secondly the GeoJSON code was exposing BOX2DFLOAT4 information to the client instead of calculating the true bounding box. With thanks to Olivier Courtin.

git-svn-id: http://svn.osgeo.org/postgis/branches/1.3@3220 b70326c6-7e19-0410-871a-916f4a2858ee