use getent(1) from glibc to retrieve user home #27

https://github.com/joeyh/etckeeper/pull/27

url for git am:
https://patch-diff.githubusercontent.com/raw/joeyh/etckeeper/pull/27.patch

> I had to guess at the motivation for this patch, which is never the best
> position for a patch to leave its receiver in.
> 
> I guess that getent is a little faster than running perl to do the same
> thing. And, getent seems to always be available, at least on debian.
> 
> So, applied, with some doubt. [[done]] --[[Joey]]