Add option "-d destdir" which instructs config to use another output

Add option "-d destdir" which instructs config to use another output
directory than the default one. If the option is not given, then the
output of config is exactly as before. Only when an alternate output
directory has been specified will config modify its behavior.

Additional changed:
o  Remove the now conflicting and unused NODEV define. It
   conflicts with NODEV in sys/param.h.
o  Rename the now conflicting MACHINE token to ARCH. It
   conflicts with MACHINE in sys/param.h.
o  Fix some easy style bugs.
o  Fix some easy grammar bugs in the manpage.

Approved by: peter, archie