[SSSD] [sssd PR#554][opened] Several fixes for the files provider

[jhrozek]

   URL: https://github.com/SSSD/sssd/pull/554
Author: jhrozek
 Title: #554: Several fixes for the files provider
Action: opened

PR body:
"""
This PR contains several fixes for the files provider, mainly a performance
bug which is really embarassing - I have no idea why was the code #if-ed
out. I think I must have been experimenting with the provider update
and then forgot to remove the preprocessor macros. The rest is mostly code
cleanup and minor fixes.

btw initially I wanted to also include a fix to avoid removing cachedPassword
on updates, but I realized the current way where the files provider throws
away everything and then updates everything would force us to maintain
all the sssd-added attributes on our own. And because especially with 2FA
it might not be just cachedPassword, but also the factor length or offline
lockout counter etc, we might as well devise a better way to update the
cache than just throw away everything and recreate the entries, so I'll work
on that separately.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/554/head:pr554
git checkout pr554