ITS#8486 use kbtree for sessionlog

Saves about 20% CPU time and RAM
3 jobs for logtavl in 33 minutes and 8 seconds (queued for 34 seconds)
Status Job ID Name Coverage
  Build
passed #2283
build-gnutls-mit

00:29:38

passed #2281
build-no-threads-no-slapd

00:03:29

passed #2282
build-openssl-heimdal

00:31:34