WateFilter depth write fix (yeah 'fix' Kirill). Issue was glClear(GL_DEPTH_BUFFER_BIT) seems to not work when glDepthMask is false

see http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=257223
Also there might be the same issue when copying frame buffers 

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@7628 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

engine/src/core/com/jme3/post/FilterPostProcessor.java

@@ -199,9 +199,6 @@ public class FilterPostProcessor implements SceneProcessor, Savable {
         r.clearBuffers(false, true, true);
         renderManager.renderGeometry(fsQuad);
 
-        //re applying default render state at the end of the render 
-        // to avoid depth write issues, MUST BE A BETTER WAY
-        r.applyRenderState(RenderState.DEFAULT);
     }
 
     public boolean isInitialized() {

engine/src/lwjgl-ogl/com/jme3/renderer/lwjgl/LwjglRenderer.java

@@ -456,6 +456,15 @@ public class LwjglRenderer implements Renderer {
             bits = GL_COLOR_BUFFER_BIT;
         }
         if (depth) {
+            
+            //glClear(GL_DEPTH_BUFFER_BIT) seems to not work when glDepthMask is false
+            //here s some link on openl board
+            //http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=257223
+            //if depth clear is requested, we enable the depthMask            
+            if (context.depthWriteEnabled == false) {
+                glDepthMask(true);
+                context.depthWriteEnabled = true;
+            }
             bits |= GL_DEPTH_BUFFER_BIT;
         }
         if (stencil) {