PostGIS intersects lookup with raster and geometry

[Emanuele Di Giacomo]

Hi,
reading the documentation, I've found that `rast__intersects=geom` is
translated to `ST_Intersects(ST_Polygon(rast), geom)`)[1], but in
PostGIS documentation I've found that it's possible to mix rasters
and geometries [2].

`ST_Intersects(raster, geom)` can be quite faster than
`ST_Intersects(ST_Polygon(raster), geom)`.

Before submitting a patch, I'd like to be sure that I'm not missing
something.

Thanks,

Emanuele


[1]: https://docs.djangoproject.com/en/1.11/ref/contrib/gis/geoquerysets/#lookups-with-rasters
[2]: https://postgis.net/docs/RT_ST_Intersects.html