Added the file, ftp, and smb downloaders to common/download.go
Added the file, ftp, and smb downloaders to common/download.go

mitchellh/packer,pieter-lazzaro/packer,KohlsTechnology/packer,tas50/packer,ricardclau/packer,mitchellh/packer,pecigonzalo/packer,hashicorp/packer,tb3088/packer,routelastresort/packer,routelastresort/packer,paulmey/packer,paulmey/packer,grubernaut/packer,p1-nico/packer,dave2/packer,dave2/packer,tb3088/packer,dave2/packer,grubernaut/packer,tas50/packer,p1-nico/packer,routelastresort/packer,tb3088/packer,mkuzmin/packer,paulmey/packer,mkuzmin/packer,KohlsTechnology/packer,paulmey/packer,KohlsTechnology/packer,dave2/packer,youhong316/packer,bryson/packer,tb3088/packer,bryson/packer,ricardclau/packer,timsutton/packer,rnaveiras/packer,p1-nico/packer,timsutton/packer,timsutton/packer,timsutton/packer,routelastresort/packer,pieter-lazzaro/packer,ChrisLundquist/packer,ChrisLundquist/packer,rnaveiras/packer,hashicorp/packer,KohlsTechnology/packer,hashicorp/packer,rnaveiras/packer,youhong316/packer,grubernaut/packer,youhong316/packer,pecigonzalo/packer,youhong316/packer,mitchellh/packer,ChrisLundquist/packer,bryson/packer,rnaveiras/packer,ChrisLundquist/packer,rnaveiras/packer,ricardclau/packer,tb3088/packer,youhong316/packer,mkuzmin/packer,mitchellh/packer,mkuzmin/packer,mkuzmin/packer,timsutton/packer,tas50/packer,tas50/packer,grubernaut/packer,youhong316/packer,ricardclau/packer,ricardclau/packer,hashicorp/packer,KohlsTechnology/packer,ChrisLundquist/packer,bryson/packer,pieter-lazzaro/packer,dave2/packer,dave2/packer,pieter-lazzaro/packer,p1-nico/packer,paulmey/packer,grubernaut/packer,ricardclau/packer,pieter-lazzaro/packer,KohlsTechnology/packer,grubernaut/packer,p1-nico/packer,rnaveiras/packer,timsutton/packer,routelastresort/packer,pieter-lazzaro/packer,bryson/packer,pecigonzalo/packer,bryson/packer,tas50/packer,tb3088/packer,p1-nico/packer,paulmey/packer,tas50/packer,pecigonzalo/packer,ChrisLundquist/packer,mkuzmin/packer,mitchellh/packer