ensure proper error messages for bundle addition
ensure proper error messages for bundle addition

chenzhenxi/jspm-cli,buddhike/jspm-cli,nfl/jspm-cli,Y--/jspm-cli,Rush/jspm-cli,apiv/jspm-cli,hmps/jspm-cli,hmps/jspm-cli,Y--/jspm-cli,cgvarela/jspm-cli,buddhike/jspm-cli,nianwang/jspm-cli,Rush/jspm-cli,jspm/jspm-cli,Y--/jspm-cli,nfl/jspm-cli,Rush/jspm-cli,nianwang/jspm-cli,cgvarela/jspm-cli,nfl/jspm-cli,jspm/jspm-cli,wichert/jspm-cli,apiv/jspm-cli,jspm/jspm-cli,hmps/jspm-cli,buddhike/jspm-cli,wichert/jspm-cli,apiv/jspm-cli,jackfranklin/jspm-cli,chenzhenxi/jspm-cli,jackfranklin/jspm-cli,nianwang/jspm-cli,wichert/jspm-cli,jackfranklin/jspm-cli,cgvarela/jspm-cli,chenzhenxi/jspm-cli