check_ram2: Add new plugin

The old check_ram plugin returns quite imprecise measurements and inconsistent performance data depending on the options set. It furthermore had problems if the system locale wasn't LANG=C. This improved version was written from scratch and supports systems with any locale set, since it relies on /proc/meminfo for data. It further allows a more consistent setting of thresholds and outputs performance data consistently.

Since this plugin is incompatible with check_ram in terms of the usage, it is added as a second monitoring plugin.