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Version Numbers in `configure'
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   The following macros manage version numbers for `configure' scripts.
Using them is optional.

 - Macro: AC_PREREQ (VERSION)
     Ensure that a recent enough version of Autoconf is being used.  If
     the version of Autoconf being used to create `configure' is earlier
     than VERSION, print an error message on the standard error output
     and do not create `configure'.  For example:

          AC_PREREQ(1.8)

     This macro is useful if your `configure.in' relies on non-obvious
     behavior that changed between Autoconf releases.  If it merely
     needs recently added macros, then `AC_PREREQ' is less useful,
     because the `autoconf' program already tells the user which macros
     are not found.  The same thing happens if `configure.in' is
     processed by a version of Autoconf older than when `AC_PREREQ' was
     added.

 - Macro: AC_REVISION (REVISION-INFO)
     Copy revision stamp REVISION-INFO into the `configure' script,
     with any dollar signs or double-quotes removed.  This macro lets
     you put a revision stamp from `configure.in' into `configure'
     without RCS or CVS changing it when you check in `configure'.  That
     way, you can determine easily which revision of `configure.in' a
     particular `configure' corresponds to.

     It is a good idea to call this macro before `AC_INIT' so that the
     revision number is near the top of both `configure.in' and
     `configure'.  To support doing that, the `AC_REVISION' output
     begins with `#! /bin/sh', like the normal start of a `configure'
     script does.

     For example, this line in `configure.in':

          AC_REVISION($Revision: 1.30 $)dnl

     produces this in `configure':

          #! /bin/sh
          # From configure.in Revision: 1.30