Fixed reporting of negative window positions.

MSDN recommends LOWORD and HIWORD for WM_MOVE, but these do not
handle negative window positions correctly.

Fixes #172.

README.md

@@ -42,6 +42,7 @@ guide in the GLFW documentation.
  - [Win32] Bugfix: The disabled cursor mode clip rectangle was updated for
                    unfocused windows
  - [Win32] Bugfix: Cursor was not properly re-centered over odd-sized windows
+ - [Win32] Bugfix: Negative window positions were reported incorrectly
  - [Cocoa] Added dependency on CoreVideo framework for refresh rate retrieval
  - [Cocoa] Enabled Lion full screen for resizable windowed mode windows
  - [Cocoa] Moved to Cocoa API for application transformation and activation

src/win32_window.c

@@ -684,7 +684,9 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
                 updateClipRect(window);
             }
 
-            _glfwInputWindowPos(window, LOWORD(lParam), HIWORD(lParam));
+            _glfwInputWindowPos(window,
+                                GET_X_LPARAM(lParam),
+                                GET_Y_LPARAM(lParam));
             return 0;
         }