MFC 251637:

MFC 251637:
Borrow the algorithm from kvm_getprocs() to fix procstat(1) to handle the
case where the process tables grows in between the calls to fetch the size
and fetch the table.

Note that this is not a true MFC as the libprocstat library doesn't exist
in 8.x and the relevant code is in the procstat binary instead.

git-svn-id: svn://svn.freebsd.org/base/stable/8@252066 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f