MFC r311101:
libkvm - extend a bit the swap statistics field.

Change ksw_used and ksw_total to unsigned, which increases the maximum
total swap that can be displayed properly from ~8TB to ~16TB.

Obtained from: DragonflyBSD (ecc2e461)

Merge r261796 from head:
While it isn't too late and kvm_read_zpcpu() function isn't yet used
outside libkvm(3), change its order of arguments, so that it is the
same as in kvm_read().
Merge r261805 from head:
Add kvm_getncpus() to obtain mp_ncpus.

Merge r261796 from head:
While it isn't too late and kvm_read_zpcpu() function isn't yet used
outside libkvm(3), change its order of arguments, so that it is the
same as in kvm_read().
Merge r261805 from head:
Add kvm_getncpus() to obtain mp_ncpus.