src/Pure/System/progress.scala

 class Progress
 {
   def echo(msg: String) {}
   def echo_if(cond: Boolean, msg: String) { if (cond) echo(msg) }
   def theory(session: String, theory: String) {}
+
+  def echo_warning(msg: String) { echo(Output.warning_text(msg)) }
+  def echo_error(msg: String) { echo(Output.error_text(msg)) }
 
   def stopped: Boolean = false
   override def toString: String = if (stopped) "Progress(stopped)" else "Progress"
 
   def bash(script: String,