Add a couple of functions to create persistent variables that will

Add a couple of functions to create persistent variables that will
survive a sysinstall Ctrl-C -> 'Restart'.  This fixes another annoying
bug where restarting sysinstall will try to reload kernel modules and
do other external things that have already been done.  For now, use
these persistent variables to keep track of module, usbd, and pccardd
initialization.

Bug found by: rwatson
MFC after:    1 week