[issue1805] sysctl needed for taking swap statistics

[Matthew Dillon]

::The new sysctl will be useful, but i'll need to retrieve individual swap device
::stats too. Are you (or anybody else) going to create this one?
::
::In that case, can we leave this issue open until it's created?
::
::Regards.

    Ok, I took a look at FreeBSD's vm.swap_info sysctl and implemented
    something similar.  Ours is slightly different so I named it differently,
    vm.swap_info_array.  Ours takes no arguments and returns the entire
    array.

    I adjusted our libkvm code in the DragonFly HEAD so you can get example
    usage from that (/usr/src/lib/libkvm/kvm_getswapinfo.c) if you want
    to call the sysctl directly.

    Or you can use the kvm_getswapinfo() call in libkvm and it will use
    the new sysctl if it is available (presuming you recompile libkvm,
    of course, and run a fresh kernel).

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>