Adds check_memory which works like check_swap which has been updated to work like check_memory
Both sport a -u(nit) option with MB as default, like their linux versions.
A possible bug with all plugins having the -u(nit) option when using -u kB has been fixed. Don't use icinga to monitor you commodore though.
refs #8287#8060
check_swap should now be faster and more accurate, it also checks against free space instead of taken swap.
The output and CMakeLists have been updated accordingly.
fixes#8287 refs #8060