Install utilities in share/nslcd-utils
Fix getting caller's uid on password change (pynslcd)
Set FD_CLOEXEC on the client socket in utilities
Raise an error with a missing old password on password modification
Python style changes

This tries to conform more closely to PEP8. Imports have been checked and,
if used only once, moved closer to the use to avoid potential import
loops. This also includes a few other minor changes, like using __main__
for utility scripts and variable renames to avoid name clashes.