Patch TracingPrintStream to handle Kotlin IO.

Kotlins internal IO suite wraps the old System.out style, so descend
deeper in the stack when kotlin.io is detected.

src/main/java/cpw/mods/fml/common/TracingPrintStream.java

@@ -21,6 +21,7 @@
 public class TracingPrintStream extends PrintStream {
 
     private Logger logger;
+    private int BASE_DEPTH = 3;
 
     public TracingPrintStream(Logger logger, PrintStream original) {
         super(original);
@@ -39,7 +40,10 @@ public void println(String s) {
 
     private String getPrefix() {
         StackTraceElement[] elems = Thread.currentThread().getStackTrace();
-        StackTraceElement elem = elems[3]; // The caller is always at depth 2, plus this call.
+        StackTraceElement elem = elems[BASE_DEPTH]; // The caller is always at BASE_DEPTH, including this call.
+        if (elem.getClassName().startsWith("kotlin.io.")) {
+            elem = elems[BASE_DEPTH + 2]; // Kotlins IoPackage masks origins 2 deeper in the stack.
+        }
         return "[" + elem.getClassName() + ":" + elem.getMethodName() + ":" + elem.getLineNumber() + "]: ";
     }