configure.in: Rename configure.ac to fix an 'aclocal' warning

--HG--
rename : test/configure.in => test/configure.ac
diff --git a/configure b/configure
index 7f402c0..fe0dfad 100755
--- a/configure
+++ b/configure
@@ -25159,7 +25159,7 @@
         ;;
     *)
         as_fn_error $? "
-*** Unsupported host:  Please add to configure.in
+*** Unsupported host:  Please add to configure.ac
         " "$LINENO" 5
         ;;
 esac
diff --git a/test/configure.in b/test/configure.ac
similarity index 100%
rename from test/configure.in
rename to test/configure.ac