Update Makefile in terms of C# sources and keyfile command line option
Update Makefile in terms of C# sources and keyfile command line option

committer: Jon Skeet <202926418fe28ce7b8564dbdb1a543a31acbf038@pobox.com>

Livefyre/protobuf,google/protobuf,angshuman-agarwal/protobuf-csharp-port,google/protobuf,jskeet/protobuf-csharp-port,google/protobuf,Livefyre/protobuf,Livefyre/protobuf,jskeet/protobuf-csharp-port,pldg/protobuf-csharp-port,pldg/protobuf-csharp-port,google/protobuf,Livefyre/protobuf,google/protobuf,google/protobuf,jskeet/protobuf-csharp-port,google/protobuf,phofman/protobuf-csharp-port,phofman/protobuf-csharp-port,angshuman-agarwal/protobuf-csharp-port,Livefyre/protobuf,angshuman-agarwal/protobuf-csharp-port,google/protobuf,google/protobuf,google/protobuf,pldg/protobuf-csharp-port,jskeet/protobuf-csharp-port,pldg/protobuf-csharp-port,google/protobuf,phofman/protobuf-csharp-port,phofman/protobuf-csharp-port,angshuman-agarwal/protobuf-csharp-port