Clarify failed command error message indicating to run -F - close #133

lib/rscons/environment.rb

@@ -286,7 +286,7 @@ module Rscons
       unless @process_failures.empty?
         msg = @process_failures.join("\n")
         if Cache.instance["failed_commands"].size > 0
-          msg += "\nUse -F to view the failed command log from the previous build operation"
+          msg += "\nUse `#{Util.command_to_execute_me} -F` to view the failed command log from the previous build operation"
         end
         raise RsconsError.new(msg)
       end

lib/rscons/util.rb

@@ -217,6 +217,14 @@ module Rscons
         queue.pop
       end
 
+      # Command that can be run to execute this instance of rscons from the
+      # current working directory.
+      def command_to_execute_me
+        command = Pathname.new(File.expand_path($0)).relative_path_from(Dir.pwd).to_s
+        command = "./#{command}" unless command["/"]
+        command
+      end
+
       private
 
       # Check if a directory contains a certain executable.