Safety checks for polling requests lowered for increased IO.
Merge branch 'master' of github.com:openzfsonosx/spl
Initial slice allocator implementation
added new files for allocator
remove unused initalisation code.
- Small code cleanups
- Improve space efficiency
- Add time based garbage collection for returning memory to underlying OS
- Correct fault where memory was not retained once a certain working set
  size was exceeded.
And added the new files as well.