Darwin fix: if HW_MACHINE_ARCH unusable, ...

... try HW_MACHINE
improve paging stats

* use mach stats like for memory on Mach systems
* use uvmexp/evmexp_sysctl explicitely where supported and no
  dirty rough os detection based fallback like fbsd forces
  it because sysctlbyname() cannot be reasonable checked
  (think cross-compiling)