Fix #22

Thanks to @Anthiste

src/win32/ffi.rs

@@ -718,6 +718,9 @@ extern "system" {
     // http://msdn.microsoft.com/en-us/library/windows/desktop/ms633519(v=vs.85).aspx
     pub fn GetWindowRect(hWnd: HWND, lpRect: *mut RECT) -> BOOL;
 
+    //
+    pub fn glFlush();
+
     // 
     pub fn glViewport(x: libc::c_int, y: libc::c_int, w: libc::c_int, h: libc::c_int);
 

src/win32/mod.rs

@@ -191,6 +191,8 @@ impl Window {
     /// See the docs if the crate root file.
     pub fn swap_buffers(&self) {
         unsafe {
+            ffi::glFlush();
+
             if ffi::SwapBuffers(self.hdc) == 0 {
                 use std::os;
                 fail!("{}", os::error_string(os::errno()));