Reimplement unload handler. Fixes #532.
Reimplement unload handler. Fixes #532.

isaacs/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,fxtentacle/tilemill,fxtentacle/tilemill,tilemill-project/tilemill,MappingKat/tilemill,MappingKat/tilemill,tizzybec/tilemill,Zhao-Qi/tilemill,mbrukman/tilemill,MappingKat/tilemill,nyimbi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,paulovieira/tilemill-clima,MappingKat/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Zhao-Qi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,isaacs/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,tilemill-project/tilemill,nyimbi/tilemill,fxtentacle/tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,tilemill-project/tilemill,mbrukman/tilemill,isaacs/tilemill,paulovieira/tilemill-clima,nyimbi/tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,florianf/tileoven,florianf/tileoven,fxtentacle/tilemill,florianf/tileoven,mbrukman/tilemill,tizzybec/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,tizzybec/tilemill,MappingKat/tilemill,fxtentacle/tilemill,tizzybec/tilemill