Creates a tab page if it has not already been created.
User objects used as tab pages
userobject.CreatePage ( )
Integer. Returns one of the following values:1 if the page is successfully created and -1 if the page was already created or if it is not a tab page.
1 — The tab page was successfully created
0 — The tab page has already been created
-1 — The user object is not a tab page
