public void OpenProGridsPopup()
{
if (EditorUtility.DisplayDialog(
"Upgrade to ProGrids", // Title
"Enables all kinds of super-cool features, like different snap values, more units of measurement, and angles.", // Message
"Upgrade", // Okay
"Cancel" // Cancel
))
#if UNITY_4
{ AssetStore.OpenURL(PROGRIDS_UPGRADE_URL); }
#else
{ Application.OpenURL(PROGRIDS_UPGRADE_URL); }
#endif
}