Preprocessor errors should go to stderr not stdout.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@319 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/prism/Preprocessor.java

@@ -427,7 +427,7 @@ public class Preprocessor
 			}
 		}
 		catch (PrismException e) {
-			System.out.println("Error: " + e.getMessage());
+			System.err.println("Error: " + e.getMessage());
 		}
 	}
 }