fixes for linux ldap/pam to work with Cronicle

[wccropper]

This fixes the Cronicle issue jhuckaby/Cronicle#141, allowing Cronicle to run as users via ldap/pam. This should work across all linux distros as getent is part of glibc. This was tested on CentOS7. I've included the help for getent below.

getent --help

Usage: getent [OPTION...] database [key ...]
Get entries from administrative database.

-i, --no-idn disable IDN encoding
-s, --service=CONFIG Service configuration to be used
-?, --help Give this help list
--usage Give a short usage message
-V, --version Print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.

Supported databases:
ahosts ahostsv4 ahostsv6 aliases ethers group gshadow hosts initgroups
netgroup networks passwd protocols rpc services shadow

For bug reporting instructions, please see:
http://www.gnu.org/software/libc/bugs.html.

[jhuckaby]

This is awesome, thank you! Very cool pull request. I'll test this on my Linux systems this weekend and will merge if all is well.

[jhuckaby]

Works great, thank you! Merged.