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/egl/android_natives.h b/include/ui/egl/android_natives.h
index 0398ea7..a3a1316 100644
--- a/include/ui/egl/android_natives.h
+++ b/include/ui/egl/android_natives.h
@@ -60,6 +60,12 @@
 
 // ---------------------------------------------------------------------------
 
+/* attributes queriable with query() */
+enum {
+    NATIVE_WINDOW_WIDTH     = 0,
+    NATIVE_WINDOW_HEIGHT    = 1
+};
+
 struct android_native_window_t 
 {
 #ifdef __cplusplus
@@ -129,8 +135,15 @@
     int     (*queueBuffer)(struct android_native_window_t* window,
                 struct android_native_buffer_t* buffer);
 
+    /*
+     * hook used to retrieve information about the native window.
+     * 
+     * Returns 0 on success or -errno on error.
+     */
+    int     (*query)(struct android_native_window_t* window,
+            int what, int* value);
     
-    void* reserved_proc[5];
+    void* reserved_proc[4];
 };
 
 // ---------------------------------------------------------------------------