add support for perl plugins
use collectd::plugin resource and handle order and ensure parameters
add collectd-rrdtool package needed for RedHat
Merge pull request #167 from cfeskens/add-redhat-rrdtool-package

add collectd-rrdtool package needed for RedHat
correct minor lint style problems
Merge pull request #161 from ccin2p3/f/plugins-perl

add support for perl plugins
Rewrite of postgresql module to allow invocation by defined types

It now also support defining custom queries.

As a bonus, this rewrite is backward compatible (!)