add emission of error from Request#callback()
add emission of error from Request#callback()

classdojo/superagent,drinks/superagent,sutoiku/superagent,yussan/superagent,jarvisaoieong/superagent,stanzi83/superagent,targos/superagent,deltreey/superagent,kmalakoff/superagent-ls,noikiy/suberagent,killerlayup/superagent,classdojo/superagent,KuroGuo/suberagent,brotchie/superagent,brainbytes/superagent,ertrzyiks/superagent,noikiy/suberagent,deltreey/superagent,fredigato/superagent,nemisj/superagent,soyuka/superagent,jarvisaoieong/superagent,ccapndave/superagent,focusaurus/superagent,mvanlonden/superagent-webpack-client,wushuyi/superagent,modulexcite/superagent,yeatszhang/superagent,geminiyellow/superagent,kmalakoff/superagent-ls,nemisj/superagent,eligolding/superagent,puterakahfi/superagent,RubenVerborgh/superagent,stasha/superagent,drinks/superagent,aaroncrows/superagent,alinz/superagent,KingMario/superagent,h1bomb/superagent,stanzi83/superagent,ccapndave/superagent,geminiyellow/superagent,sebastianvera/superagent,bevacqua/superagent,brotchie/superagent,thejameskyle/superagent,KingMario/superagent,modulexcite/superagent,visionmedia/superagent,simonvizzini/superagent,aaroncrows/superagent,philipshurpik/superagent,yeatszhang/superagent,andyburke/superagent,soyuka/superagent,wushuyi/superagent,sutoiku/superagent,andyburke/superagent,h1bomb/superagent,brainbytes/superagent,ertrzyiks/superagent,craigspaeth/superagent,RubenVerborgh/superagent,zsh2938/superagent,fredigato/superagent,visionmedia/superagent,alinz/superagent,simonvizzini/superagent,stasha/superagent,thejameskyle/superagent,focusaurus/superagent,craigspaeth/superagent,sebastianvera/superagent,zsh2938/superagent,reinaldo13/superagent,philipshurpik/superagent,targos/superagent,KuroGuo/suberagent,puterakahfi/superagent,yussan/superagent,eligolding/superagent,killerlayup/superagent,mvanlonden/superagent-webpack-client,reinaldo13/superagent,visionmedia/superagent