Added window position callback.

src/internal.h

diff --git a/src/internal.h b/src/internal.h
index c5a40af..2ef8f10 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -199,6 +199,7 @@
     int       glRobustness;
     PFNGLGETSTRINGIPROC GetStringi;
 
+    GLFWwindowposfun     windowPosCallback;
     GLFWwindowsizefun    windowSizeCallback;
     GLFWwindowclosefun   windowCloseCallback;
     GLFWwindowrefreshfun windowRefreshCallback;

src/window.c

diff --git a/src/window.c b/src/window.c
index 908a2a7..ac0fd02 100644
--- a/src/window.c
+++ b/src/window.c
@@ -119,8 +119,14 @@
 
 void _glfwInputWindowPos(_GLFWwindow* window, int x, int y)
 {
+    if (window->positionX == x && window->positionY == y)
+        return;
+
     window->positionX = x;
     window->positionY = y;
+
+    if (window->windowPosCallback)
+        window->windowPosCallback(window, x, y);
 }
 
 
@@ -765,6 +771,24 @@
 
 
 //========================================================================
+// Set callback function for window position changes
+//========================================================================
+
+GLFWAPI void glfwSetWindowPosCallback(GLFWwindow handle, GLFWwindowposfun cbfun)
+{
+    _GLFWwindow* window = (_GLFWwindow*) handle;
+
+    if (!_glfwInitialized)
+    {
+        _glfwSetError(GLFW_NOT_INITIALIZED, NULL);
+        return;
+    }
+
+    window->windowPosCallback = cbfun;
+}
+
+
+//========================================================================
 // Set callback function for window size changes
 //========================================================================