Change the implementation of RETURNING for SDO_GEOMETRY so that it works
(somewhat; I am still waiting for feedback from Oracle as to how to handle this correctly).
Add a cached SDO_GEOMETRY NULL value for return by the input callback.
The output callback returns the address of a NULL pointer so that Oracle allocates memory for the return value.
Geometry output columns are bound only once to avoid errors that I don't quite understand.
Add an error context to geometry conversion calls to track errors better.
More changes (hopefully improvements) to oracle_gis.c.
- Report the Oracle error as detail message wherever appropriate.
- Remove the oracleDebug2 calls as they seem to have been there only for debugging purposes.
- Remove #include of stdint.h and replace the uint*_t with Oracle's ub*.
  PostgreSQL code is not supposed to rely on C99 features, and I am not sure if all compilers supported by Oracle guarantee C99.
- Test values retrieved with OCICollGetElem for NULL-ness.
- Add a comment where the PostGIS to Oracle conversion of multipolygons should be.