Create a global variable that marks geofield as using the new schema / WKB

I'm starting to write integration for geocoder, and I think for most other modules that integrate with geofield, we need to be able to detect wether we are running an "old" version of geofield, or wether we are running the new, WKB powered one.

I think a global variable makes the most sense. It'll either be NULL if it's an older version (not defined), or TRUE if it's the new one with the new schema.

I'm thinking something like global $geofield_geom_schema = TRUE