Set a marker system property on applications when they're run through getdown.

Also: good style is to use the result of Collection.toArray(), not the
array you pass it. There is no guarantee it will *use* your array...

src/java/com/threerings/getdown/data/Application.java

@@ -782,6 +782,9 @@ public class Application
             args.add("-Dhttp.proxyPort=" + System.getProperty("http.proxyPort"));
         }
 
+        // add the marker indicating the app is running in getdown
+        args.add("-D" + Properties.GETDOWN + "=true");
+
         // pass along any pass-through arguments
         for (Map.Entry<Object, Object> entry : System.getProperties().entrySet()) {
             String key = (String)entry.getKey();
@@ -806,8 +809,7 @@ public class Application
 
 
         String[] envp = createEnvironment();
-        String[] sargs = new String[args.size()];
-        args.toArray(sargs);
+        String[] sargs = args.toArray(new String[args.size()]);
         log.info("Running " + StringUtil.join(sargs, "\n  "));
 
         return Runtime.getRuntime().exec(sargs, envp);

src/java/com/threerings/getdown/data/Properties.java

@@ -0,0 +1,32 @@
+//
+// $Id$
+// Getdown - application installer, patcher and launcher
+// Copyright (C) 2004-2010 Three Rings Design, Inc.
+//
+// Redistribution and use in source and binary forms, with or without modification, are permitted
+// provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+//    conditions and the following disclaimer in the documentation and/or other materials provided
+//    with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+// PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+// INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+// TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+package com.threerings.getdown.data;
+
+/**
+ * System property constants associated with Getdown.
+ */
+public class Properties
+{
+    /** This property will be set to "true" on the application when it is being run by getdown. */
+    public static final String GETDOWN = "com.threerings.getdown";
+}