Adds missing key code for Print Screen (#682) (#806)

* Adds missing key code for Print Screen and update javadoc (#682)

jme3-core/src/main/java/com/jme3/input/KeyInput.java

@@ -445,6 +445,16 @@ public interface KeyInput extends Input {
      * (J3100).
      */
     public static final int KEY_UNLABELED = 0x97;
+    /**
+     * PrtScr key.
+     * Note: for use on keyboards with a PrtScr key that is
+     * separate from the SysRq key. Most keyboards combine
+     * SysRq and PrtScr so if the intent is to actually
+     * capture the user's desire to capture the screen
+     * then SysRq is the most likely scan code.
+     * Use PrtScr to catch the rest (laptops, mini-keyboards, etc.)
+     */
+    public static final int KEY_PRTSCR = 0x9A;
     /**
      * Enter key (num pad).
      */

jme3-desktop/src/main/java/com/jme3/input/awt/AwtKeyInput.java

@@ -371,6 +371,8 @@ public class AwtKeyInput implements KeyInput, KeyListener {
                 return KeyEvent.VK_ALT; //todo: location left
             case KEY_RMENU:
                 return KeyEvent.VK_ALT; //todo: location right
+            case KEY_PRTSCR:
+                return KeyEvent.VK_PRINTSCREEN;
         }
         logger.log(Level.WARNING, "unsupported key:{0}", key);
         return 0x10000 + key;
@@ -600,6 +602,8 @@ public class AwtKeyInput implements KeyInput, KeyListener {
                 return KEY_LMENU; //Left vs. Right need to improve
             case KeyEvent.VK_META:
             	return KEY_RCONTROL;
+            case KeyEvent.VK_PRINTSCREEN:
+                return KEY_PRTSCR;
 
         }
         logger.log( Level.WARNING, "unsupported key:{0}", key);