Revert "Removed internal limit 2^20 for lloctree"

This reverts commit 7376c833c70fa8253ca4cd0f2f5fc2ed9bd76f49.
Increased octree limit to 32k. Addresses "4096 bug" in Opensim

Thanks to NickyD for tracking down the cause.

Refereces:

https://jira.secondlife.com/browse/SVC-2941
http://redmine.kokuaviewer.org/issues/465
http://jira.phoenixviewer.com/browse/FIRE-11593