libspatialite: add head and geopackage options

**Note**: head build requires removal of head url line from fossil.rb, i.e. requires https://github.com/Homebrew/homebrew/pull/25605 to be committed.

The `--with-geopackage` option is for recently improved support for the proposed [OGC GeoPackage](http://www.ogcnetwork.net/geopackage), a significant new open-source geospatial standard. See also: [spatialite list post](https://groups.google.com/forum/#!topic/spatialite-users/Z4-qBOT4TFI). The option is also valid (though outdated) for current stable 4.1.1 version.