(ITS#8625) Separate tavl and avl types

[okuznik@symas.com]

Full_Name: Ondrej Kuznik
Version: master
OS: 
URL: ftp://ftp.openldap.org/incoming/Ondrej-Kuznik-20170329a-Separate-Avlnode-and-TAvlnode-types.patch
Submission from: (NULL) (2a02:c7f:2247:ec00:a3e:8eff:fe52:dac5)


Since it is not safe to run any of the avl_* functions on a tavl node, it would
be useful to separate the types to prevent hard to diagnose issues caused by a
simple typo.

The provided patch against master separates the two types and adjusts the tavl
users.