Fix output georeference on warping rasters with default georeference

Closes #2911 and re-closes #2251

git-svn-id: http://svn.osgeo.org/postgis/trunk@12928 b70326c6-7e19-0410-871a-916f4a2858ee
Implement ST_CreateRasterOverview (#2247)

Drafted test, in progress