Avoid using UI if we're in a headless JVM.

Closes #131.

CHANGELOG.md

@@ -12,6 +12,10 @@
   Getdown. They must be prefixed by `sys.`: for example `sys.silent = true` will set the `silent`
   system property to `true`.
 
+* If Getdown is run in a headless JVM, it will avoid showing a UI but will attempt to install and
+  launch the application anyhow. Note that passing `-Dsilent` will override this behavior (because
+  in silent mode the default is only to install the app, not also launch it).
+
 * Fixed issue with `appid` not being properly used when specified via command line arg.
 
 * Fixed issue with running Getdown on single CPU systems (or virtual systems). It was attempting to

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

@@ -9,6 +9,7 @@ import java.awt.BorderLayout;
 import java.awt.Container;
 import java.awt.Dimension;
 import java.awt.EventQueue;
+import java.awt.GraphicsEnvironment;
 import java.awt.Image;
 import java.awt.event.ActionEvent;
 import java.awt.image.BufferedImage;
@@ -67,6 +68,13 @@ public abstract class Getdown extends Thread
             if (_silent) {
                 _launchInSilent = SysProps.launchInSilent();
             }
+            // If we're running in a headless environment and have not otherwise customized
+            // silence, operate without a UI and do launch the app.
+            if (!_silent && GraphicsEnvironment.isHeadless()) {
+                log.info("Running in headless JVM, will attempt to operate without UI.");
+                _silent = true;
+                _launchInSilent = true;
+            }
             _delay = SysProps.startDelay();
         } catch (SecurityException se) {
             // don't freak out, just assume non-silent and no delay; we're probably already