Add enum34 to requirements.
Add enum34 to requirements.

Should be harmless on Python 3.4.

Closes #149.

youngpm/rasterio,njwilson23/rasterio,clembou/rasterio,njwilson23/rasterio,johanvdw/rasterio,brendan-ward/rasterio,perrygeo/rasterio,johanvdw/rasterio,clembou/rasterio,perrygeo/rasterio,njwilson23/rasterio,brendan-ward/rasterio,snorfalorpagus/rasterio,perrygeo/rasterio,kapadia/rasterio,kapadia/rasterio,clembou/rasterio,brendan-ward/rasterio,youngpm/rasterio,kapadia/rasterio,johanvdw/rasterio,youngpm/rasterio,sgillies/rasterio