exports: avoid setting model's 'complete' too early - closes #1389, #1404, and #1405
exports: avoid setting model's 'complete' too early - closes #1389, #1404, and #1405

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