various system information.
* Implemented retrieving some VM stats via this call.
* The VM now maintains a page fault counter, and sets system_info::page_faults
accordingly.
* Added a (pretty simple) "vmstat" command line app.
* Minor cleanup.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27597 a95241bf-73f2-0310-859d-f6bbb57e9c96
