This adds support for versions of FreeIPMI before 1.2 (without the
threshold information), and explicits the dependency information.
It also works with older Munin nodes where dirtyconfig is not supported.
This new plugin is written in Perl rather than sh+awk, executes
ipmi-sensors only once per call (config/fetch still require two calls
total), and with one call it produces all the available graphs
depending on the available sensors.
This still allows for monitoring a remote system, and that becomes
even more interesting since it only fetches data once.
The plugin will also now fail autoconf if there is no sensor output
that can be monitored.
