memory-constraints-20180406-bp155.2.13

- Use the correct macro %_rpmmacrodir in the %files section.

- Take SwapTotal into account, MemTotal only reflects physical memory. Some
  workers have a considerable amount of swap.

- Fix the macros to define default value if _threads are not defined
  to fallback to amount of CPUs

- Use install instead of mkdir and cp

- Update description to contain less typos

- Initial package to ensure restrictions on jobs when building
  huge packages