Avoid samskivert StringUtil import.

I thought I excised all of these except the Swing stuff, but apparently not.
I will finish that job.

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

@@ -31,12 +31,11 @@ import javax.swing.WindowConstants;
 import com.samskivert.swing.util.SwingUtil;
 import com.samskivert.util.ArrayUtil;
 import com.samskivert.util.RunAnywhere;
-import com.samskivert.util.StringUtil;
 
 import com.threerings.getdown.data.Digest;
 import com.threerings.getdown.data.SysProps;
+import com.threerings.getdown.util.StringUtil;
 import static com.threerings.getdown.Log.log;
-import static com.threerings.getdown.util.StringUtil.couldBeValidUrl;
 
 /**
  * The main application entry point for Getdown.
@@ -195,7 +194,7 @@ public class GetdownApp
 
             @Override
             protected void showDocument (String url) {
-                if (!couldBeValidUrl(url)) {
+                if (!StringUtil.couldBeValidUrl(url)) {
                     // command injection would be possible if we allowed e.g. spaces and double quotes
                     log.warning("Invalid document URL.", "url", url);
                     return;