Include WT_PAGE_ROW_INT and WT_PAGE_COL_INT looks wrong to me, it's not possible to split internal pages, is it?

And, not sure why we're naming the page variable `orig`, and not `page` in this function?

```
       return (page->type == WT_PAGE_ROW_LEAF ?
                __split_row_page_inmem(session, orig) : EBUSY);
```

may be sufficient, and this function may not be needed?