Bug 47991

	<http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html#AEN27243> says after "make installworld" one should boot single-user to verify the new kernel works, but not how to perform this verification:

      <div class="SECT2">
        <h2 class="SECT2"><a id="AEN27243" name="AEN27243">21.4.8
        Reboot into Single User Mode</a></h2>

        <p>You should reboot into single user mode to test the new
        kernel works. Do this by following the instructions in <a
        href="makeworld.html#MAKEWORLD-SINGLEUSER">Section
        21.4.4</a>.</p>
      </div>

	I had previously thought I should verify the functionality of ps and friends, but I just did an installworld and broke ps. I now think this is simply an indication of the kernel having evolved, and installworld would clear the problem up, but the Handbook (and UPDATING) should have some information on what to test at this stage, and probably at minimum a reference to <http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig-trouble.html> for tips on backing out a bad kernel.

Fix: 

Clarify what to look for after make installkernel and before make installworld, and exit strategies if things go in the pot.
How-To-Repeat: 	Rebuild a kernel, read the Handbook, and try to determine if all is well or busted after "make installkernel" and reboot.