Add option to rescale flux source pulses.

This actually scales by the reciprotal of the flux sink, to
allow the same value to be set for both options.

lib/fluxsource/fluxsource.proto

@@ -39,6 +39,7 @@ message Fl2FluxSourceProto {
 }
 
 message FluxSourceProto {
+	optional double rescale = 9 [ default = 1.0, (help) = "amount to divide pulse periods by" ];
 	oneof source {
 		string fluxfile = 1 [default = "name of source flux file"];
 		HardwareFluxSourceProto drive = 2;