NagiosPerfdataCollector (plus bonus minor improvements to MountStatsCollector)

I've decided it's probably dumb for me to maintain Metricinga as a separate daemon, especially seeing as it's written in Python anyway, so I've ported the core code for parsing PNP4Nagios/Graphios-style Nagios performance data over to Diamond. Documentation is presently lacking, but hopefully someone finds it useful enough in its current state anyway. Enjoy!