make `_injector` a function and use new `_injector()` to avoid accumulation properties when registring classes
make `_injector` a function and use new `_injector()` to avoid accumulation properties when registring classes

mapnik/python-mapnik,mapnik/python-mapnik,mapnik/python-mapnik,tomhughes/python-mapnik,tomhughes/python-mapnik,mapycz/python-mapnik,mapycz/python-mapnik,tomhughes/python-mapnik