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/include/ui/FramebufferNativeWindow.h b/include/ui/FramebufferNativeWindow.h
index e72357a..cb9bf94 100644
--- a/include/ui/FramebufferNativeWindow.h
+++ b/include/ui/FramebufferNativeWindow.h
@@ -62,6 +62,7 @@
     static int dequeueBuffer(android_native_window_t* window, android_native_buffer_t** buffer);
     static int lockBuffer(android_native_window_t* window, android_native_buffer_t* buffer);
     static int queueBuffer(android_native_window_t* window, android_native_buffer_t* buffer);
+    static int query(android_native_window_t* window, int what, int* value);
     
     framebuffer_device_t* fbDev;
     alloc_device_t* grDev;