configure: supermin should be listed as AC_PATH_PROG, since it is used at run time.

See top of configure.ac:

 > # NB: AC_CHECK_PROG(S) or AC_PATH_PROG(S)?
 > # Use AC_CHECK_PROG(S) for programs which are only used during build.
 > # Use AC_PATH_PROG(S) for program names which are compiled into the
 > # binary and used at run time.  The reason is so that we know which
 > # programs the binary actually uses.