Adding pages with a lot of sibling pages performs poorly

Adding pages to a space where the new page has a lot of sibling pages performs poorly. The performance degrades linearly as more siblings are added. From my testing an empty space took 10ms to add a page, but a space with 10,000 root level pages took 1 second to add a single page via SOAP or XML-RPC. It also has the potential to cause an OutOfMemoryError.

This occurs because of the fix for CONF-14681, which loads all the sibling pages to determine if they are ordered and if they are, what the new page's position should be. This is easily replaced by code that looks up the highest position value for that level of the page tree.