at first I commented out the /sbin/ldconfig line in rc.M file... (is that important? it consumes to much time, I think..)
If I were you I should not edit the /etc/rc.d/ files especially if you ask this type of question.
run ldconfig is for update links with shared libraries. shared libraries are libraries of fonctions used by your programs if you don't update links config, programs could not find shared libraries and won't run. I suggest remove comment in rc.M file.
You can run ldconfig as root after installing new libraries so you won't have to reboot to update ld links.