Refactored the GEOS interface. Improvements include:

* Geometries now allow list-like manipulation, e.g., can add, insert, delete vertexes (or other geometries in collections) like Python lists.  Thanks, Aryeh Leib Taurog.
* Added support for GEOS prepared geometries via `prepared` property.  Prepared geometries significantly speed up certain operations.
* Added support for GEOS cascaded union as `MultiPolygon.cascaded_union` property.
* Added support for GEOS line merge as `merged` property on `LineString`, and `MultiLineString` geometries.  Thanks, Paul Smith.
* No longer use the deprecated C API for serialization to/from WKB and WKT.  Now use the GEOS I/O classes, which are now exposed as `WKTReader`, `WKTWriter`, `WKBReader`, and `WKBWriter` (which supports 3D and SRID inclusion)
* Moved each type of geometry to their own module, eliminating the cluttered `geometries.py`.
* Internally, all C API methods are explicitly called from a module rather than a star import.

Fixed #9557, #9877, #10222


git-svn-id: http://code.djangoproject.com/svn/django/trunk@10131 bcc190cf-cafb-0310-a4f2-bffc1f526a37