Rename configure.in to configure.ac, twice

* configure.ac: Rename from configure.in.
* GUILE-VERSION: Update comments; nfc.
* HACKING: Likewise.

* guile-readline/configure.ac: Rename from guile-readline/configure.in.
* guile-readline/LIBGUILEREADLINE-VERSION: Update comments; nfc.

* libguile/__scm.h: Likewise.
* libguile/gen-scmconfig.c: Likewise.
* libguile/gen-scmconfig.h.in: Likewise.

GUILE-VERSION

@@ -13,7 +13,7 @@ PACKAGE=guile
 
 # All of the shared lib versioning info.  Right now, for this to work
 # properly, you'll also need to add AC_SUBST calls to the right place
-# in configure.in, add the right -version-info statement to your
+# in configure.ac, add the right -version-info statement to your
 # Makefile.am The only library not handled here is
 # guile-readline/libguile-readline.  It is handled in
 # ./guile-readline/LIBGUILEREADLINE-VERSION.

HACKING

@@ -184,7 +184,7 @@ most lenient compiler they can find.  :)
 - If you add code which uses functions or other features that are not
 entirely portable, please make sure the rest of Guile will still
 function properly on systems where they are missing.  This usually
-entails adding a test to configure.in, and then adding #ifdefs to your
+entails adding a test to configure.ac, and then adding #ifdefs to your
 code to disable it if the system's features are missing.
 
 - The normal way of removing a function, macro or variable is to mark

guile-readline/LIBGUILEREADLINE-VERSION

@@ -2,9 +2,9 @@
 
 # This file contains the shared library versioning information.  Right
 # now, for this to work properly, you'll also need to add AC_SUBST
-# calls to the right place in configure.in, add the right
+# calls to the right place in configure.ac, add the right
 # -version-info statement to your Makefile.am, and add a call to
-# source this file from configure.in.  Later we may automate more of
+# source this file from configure.ac.  Later we may automate more of
 # this.
 
 LIBGUILEREADLINE_MAJOR=17

libguile/__scm.h

@@ -32,7 +32,7 @@
  namespace (via adding #define, typedef, or similar to this file) with
  generic names.  This usually means that any new names should be
  prefixed by either SCM_ or GUILE_.  i.e. do *not* #define HAVE_FOO or
- SIZEOF_BAR.  See configure.in, gen-scmconfig.h.in, and
+ SIZEOF_BAR.  See configure.ac, gen-scmconfig.h.in, and
  gen-scmconfig.c for examples of how to properly handle this issue.
  The main documentation is in gen-scmconfig.c.
 

libguile/gen-scmconfig.c

@@ -7,7 +7,7 @@
   Guile has four core headers:
 
     config.h: Guile's private automatically generated configuration
-      header -- generated by configure.in and autoheader.  *NOT*
+      header -- generated by configure.ac and autoheader.  *NOT*
       installed during "make install" and so may not be referred to by
       any public headers.
 
@@ -22,7 +22,7 @@
       the contents of libguile/scmconfig.h.top with the output from
       libguile/gen-scmconfig.  gen-scmconfig bases its output on the
       information in the private config.h header, the contents of
-      gen-scmconfig.h (which is created by configure.in from
+      gen-scmconfig.h (which is created by configure.ac from
       gen-scmconfig.h.in), and the information provided in this file,
       gen-scmconfig.c.
 
@@ -62,9 +62,9 @@
      scmconfig.h.
 
    - in cases where you need to communicate information from
-     configure.in to gen-scmconfig.c, don't add an AC_DEFINE unless
+     configure.ac to gen-scmconfig.c, don't add an AC_DEFINE unless
      you need it for other purposes.  Just add a suitable SCM_I_GSC_*
-     variable to configure.in, set the value, AC_SUBST the value, and
+     variable to configure.ac, set the value, AC_SUBST the value, and
      add an appropriate line to gen-scmconfig.h.in.  All gen-scmconfig
      related AC_SUBST vars should be prefixed with SCM_I_GSC_.
 
@@ -132,7 +132,7 @@ int
 main (int argc, char *argv[])
 {
   pf ("/* This file is automatically generated --"
-      " see configure.in for details */\n"
+      " see configure.ac for details */\n"
       "\n"
       "#ifndef SCM_SCMCONFIG_H\n"
       "#define SCM_SCMCONFIG_H\n");

libguile/gen-scmconfig.h.in

@@ -1,4 +1,4 @@
-/* This file is automatically generated via configure.in. */
+/* This file is automatically generated via configure.ac. */
 
 /* This is the private include header for gen-scmconfig.  See
    gen-scmconfig.c for details.  This file should be considered even