Generate Build.java file with data from the build.

Currently includes build version and time, but additional build-time static
data can be easily added in the future.

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

@@ -47,6 +47,7 @@ import com.samskivert.util.StringUtil;
 
 import com.threerings.getdown.data.Application.UpdateInterface.Step;
 import com.threerings.getdown.data.Application;
+import com.threerings.getdown.data.Build;
 import com.threerings.getdown.data.Resource;
 import com.threerings.getdown.data.SysProps;
 import com.threerings.getdown.net.Downloader;
@@ -150,6 +151,8 @@ public abstract class Getdown extends Thread
             return;
         }
 
+        log.info("Getdown starting", "version", Build.version(), "built", Build.time());
+
         // determine whether or not we can write to our install directory
         File instdir = _app.getLocalPath("");
         if (!instdir.canWrite()) {