Making PATH precious?

[Akim Demaille]

What about making PATH a precious variable?  This way, we will be able
to notice when two runs are performed with different PATH.  It would
also make

        PATH=foo ./configure

similar to

        ./configure PATH=foo

i.e., ./config.status --recheck will _preserve_ the value of PATH.


Now the bad effect is:

1. PATH will automagically appear in Automake's Makefile.in because
autoconf AC_SUBST the precious vars and all the AC_SUBST vars are
automagically put in Makefile.in.

2. PATH will appear on the command line each time ./config.status
--recheck is relaunched.  For instance:

/tmp % cat configure.ac                                          nostromo 10:57
AC_INIT
AC_ARG_VAR([PATH], [where to find the executables])
AC_OUTPUT
/tmp % autoconf                                                  nostromo 10:57
/tmp % ./configure                                               nostromo 10:57
configure: creating ./config.status
/tmp % ./config.status --recheck                                 nostromo 10:57
running /bin/sh ./configure  
PATH=/home/lrde/prof/akim/bin:/home/lrde/lrde/usr/bin:/home/lrde/prof/akim/bin:/home/lrde/lrde/usr/bin:/home/lrde/prof/akim/bin:/home/lrde/lrde/usr/bin:/home/lrde/prof/akim/bin:/home/lrde/lrde/usr/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:/usr/X11R6/bin:/usr/local/kde/bin:/usr/local/jdk/bin
  --no-create --no-recursion
configure: creating ./config.status