Log Message:
Update to 4.6.0.  NOTE ESPECIALLY the behavior change in the first
bullet below.

4.6.0 Release Notes
-------------------

 o MAJOR: Rework pj_transform() to avoid applying ellipsoid to ellipsoid
   transformations as a datum shift when no datum info is available.

 o Avoid applying "change of ellipsoid" during datum shifting based on
   ellipsoids getting changed to spheres for spherical projections.

 o Upgrade to EPSG 6.13

 o Added "900913" "Google Mercator" code in nad/esri.extra.

 o Avoid some static variable based multi-threading problems.

 o Improve error recovery if ctable style datum shift grid fails to load.

 o Support drive letters properly in PROJ_LIB paths for win32.

 o Fix occasional problem with DMS parsing.

 o Removed non-functional mpoly projection.

 o add lonlat, and latlon as aliases for longlat.