fixed some issues with the software renderer when surfaces are made current.

there was several issues:
- when a surface was made non-current, the last frame wasn't shown and the buffer could stay locked
- when a surface was made current the 2nd time, it would not dequeue a new buffer

now, queue/dequeue are done when the surface is made current.

for this to work, a new query() hook had to be added on android_native_window_t, it allows to retrieve some attributes of a window (currently only width and height).
diff --git a/opengl/libagl/egl.cpp b/opengl/libagl/egl.cpp
index 7afcae7..b0e54d8 100644
--- a/opengl/libagl/egl.cpp
+++ b/opengl/libagl/egl.cpp
@@ -216,8 +216,8 @@
     virtual     EGLBoolean  bindReadSurface(ogles_context_t* gl);
     virtual     void        connect();
     virtual     void        disconnect();
-    virtual     EGLint      getWidth() const    { return buffer->width;  }
-    virtual     EGLint      getHeight() const   { return buffer->height; }
+    virtual     EGLint      getWidth() const    { return width;  }
+    virtual     EGLint      getHeight() const   { return height; }
     virtual     EGLint      getHorizontalResolution() const;
     virtual     EGLint      getVerticalResolution() const;
     virtual     EGLint      getRefreshRate() const;
@@ -365,26 +365,8 @@
     
     // keep a reference on the window
     nativeWindow->common.incRef(&nativeWindow->common);
-
-    // dequeue a buffer
-    nativeWindow->dequeueBuffer(nativeWindow, &buffer);
-
-    // allocate a corresponding depth-buffer
-    width = buffer->width;
-    height = buffer->height;
-    if (depthFormat) {
-        depth.width   = width;
-        depth.height  = height;
-        depth.stride  = depth.width; // use the width here
-        depth.data    = (GGLubyte*)malloc(depth.stride*depth.height*2);
-        if (depth.data == 0) {
-            setError(EGL_BAD_ALLOC, EGL_NO_SURFACE);
-            return;
-        }
-    }
-
-    // keep a reference on the buffer
-    buffer->common.incRef(&buffer->common);
+    nativeWindow->query(nativeWindow, NATIVE_WINDOW_WIDTH, &width);
+    nativeWindow->query(nativeWindow, NATIVE_WINDOW_HEIGHT, &height);
 }
 
 egl_window_surface_v2_t::~egl_window_surface_v2_t() {
@@ -402,6 +384,26 @@
 
 void egl_window_surface_v2_t::connect() 
 {
+    // dequeue a buffer
+    nativeWindow->dequeueBuffer(nativeWindow, &buffer);
+
+    // allocate a corresponding depth-buffer
+    width = buffer->width;
+    height = buffer->height;
+    if (depth.format) {
+        depth.width   = width;
+        depth.height  = height;
+        depth.stride  = depth.width; // use the width here
+        depth.data    = (GGLubyte*)malloc(depth.stride*depth.height*2);
+        if (depth.data == 0) {
+            setError(EGL_BAD_ALLOC, EGL_NO_SURFACE);
+            return;
+        }
+    }
+
+    // keep a reference on the buffer
+    buffer->common.incRef(&buffer->common);
+
     // Lock the buffer
     nativeWindow->lockBuffer(nativeWindow, buffer);
     // pin the buffer down
@@ -420,6 +422,16 @@
         bits = NULL;
         unlock(buffer);
     }
+    // enqueue the last frame
+    nativeWindow->queueBuffer(nativeWindow, buffer);
+    if (buffer) {
+        buffer->common.decRef(&buffer->common);
+        buffer = 0;
+    }
+    if (previousBuffer) {
+        previousBuffer->common.decRef(&previousBuffer->common); 
+        previousBuffer = 0;
+    }
 }
 
 status_t egl_window_surface_v2_t::lock(