(ITS#8486) Syncprov sessionlog is inefficient, kills perf

[quanah@openldap.org]

Full_Name: Quanah Gibson-Mount
Version: 2.4.44
OS: Linux 2.6
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (75.111.52.177)


After setting the sessionlog for syncprov to a large size so as to avoid
ITS#8125.  However, due to the sessionlog being a linear linked list, it can be
vastly inefficient to iterate, and slows down the master to the point that
searches can time out.

Howard suggests converting it into a tree instead to help obviate the load this
currently induces.