Improve performance of check_mem bash script by reducing the number of process forks required
Change stacking of charge and add warning and critical lines
Change chart key to be more explanatory
Rename check_mem.sh to install name check_mem
Rename check_nrpe_memory.php to check_mem.php which will match pnp4nagios with CUSTOM_TEMPLATE=1 setting and nrpe command name 'check_mem'