Use a debug system property to control debugging.

When set, it disables stdout/stderr redirection and uses java.exe on Windows so
that a console window is shown with output from the launched app.

This removes the use of a debug.txt file.

launcher/src/main/java/com/threerings/getdown/launcher/GetdownApp.java

@@ -66,7 +66,7 @@ public class GetdownApp
         }
 
         // pipe our output into a file in the application directory
-        if (!SysProps.noLogRedir()) {
+        if (!SysProps.noLogRedir() && !SysProps.debug()) {
             File logFile = new File(envc.appDir, "launcher.log");
             try {
                 PrintStream logOut = new PrintStream(