Please review: Issue 5661 - LMDB hangs while Rebuilding the replication changelog RUV

[Pierre Rogier]

https://github.com/389ds/389-ds-base/pull/5676

Note for reviewer most important changes are in cl5_api.c and I find that
github diff is hard to understand for this file.
So I advise the reviewer to look at the original file beside the modified
one (i.e using a tool like meld) starting from the end of the file and
moving backward to the top of the file.

The changes in the backend are about adding a new dbimpl api function
  that iterate on a cursor calling a callback with key, value pair

The good news is that nearly all the tests are passing (in less than 2
hours)
and the 3 issues that are reported ( 1 about clu impacting both bdb and
lmdb and two operation failures in bdb tests) are not related to changelog
operation.
IMHO they are regressions about other changes.