Add the ability to pass an additional source on the command line
Add the ability to pass an additional source on the command line

This is similar to what we have in corefx and is a way to add a local
package source to the build without having to hack dir.props every time.

chcosta/core-setup,weshaggard/core-setup,chcosta/core-setup,crummel/dotnet_core-setup,steveharter/core-setup,janvorli/core-setup,joperezr/core-setup,crummel/dotnet_core-setup,janvorli/core-setup,steveharter/core-setup,ravimeda/core-setup,vivmishra/core-setup,ramarag/core-setup,ericstj/core-setup,janvorli/core-setup,MichaelSimons/core-setup,gkhanna79/core-setup,ramarag/core-setup,ravimeda/core-setup,rakeshsinghranchi/core-setup,joperezr/core-setup,crummel/dotnet_core-setup,gkhanna79/core-setup,crummel/dotnet_core-setup,weshaggard/core-setup,weshaggard/core-setup,ramarag/core-setup,MichaelSimons/core-setup,vivmishra/core-setup,chcosta/core-setup,joperezr/core-setup,zamont/core-setup,steveharter/core-setup,steveharter/core-setup,ravimeda/core-setup,MichaelSimons/core-setup,weshaggard/core-setup,rakeshsinghranchi/core-setup,ericstj/core-setup,vivmishra/core-setup,joperezr/core-setup,chcosta/core-setup,rakeshsinghranchi/core-setup,wtgodbe/core-setup,janvorli/core-setup,weshaggard/core-setup,ravimeda/core-setup,MichaelSimons/core-setup,MichaelSimons/core-setup,ravimeda/core-setup,zamont/core-setup,ericstj/core-setup,gkhanna79/core-setup,zamont/core-setup,vivmishra/core-setup,steveharter/core-setup,joperezr/core-setup,wtgodbe/core-setup,wtgodbe/core-setup,chcosta/core-setup,janvorli/core-setup,rakeshsinghranchi/core-setup,ramarag/core-setup,crummel/dotnet_core-setup,zamont/core-setup,gkhanna79/core-setup,crummel/dotnet_core-setup,vivmishra/core-setup,MichaelSimons/core-setup,vivmishra/core-setup,zamont/core-setup,ericstj/core-setup,ravimeda/core-setup,ericstj/core-setup,gkhanna79/core-setup,zamont/core-setup,wtgodbe/core-setup,wtgodbe/core-setup,rakeshsinghranchi/core-setup,ericstj/core-setup,steveharter/core-setup,ramarag/core-setup,ramarag/core-setup,wtgodbe/core-setup,gkhanna79/core-setup,janvorli/core-setup,rakeshsinghranchi/core-setup,chcosta/core-setup,weshaggard/core-setup,joperezr/core-setup