small improvements

Hi,

Seeing your recent commits on the no_kadmin branch (which I'm excited about, btw!) reminded me that I never got around to opening a pull request for this. I have been running this code in production for upwards of 6 months.

ea850d5 merges from smbk5pwd the support for updating shadowLastChange in the overlay. Otherwise it has to be done by every client.
2636b23 uses libtool for a more complete 'make clean'.
d970a4c allows slapd.conf to be used instead of cn=config (fixes #2).