Switch to autoconf 2.73.

* autogen.sh: Update comment.
* libcharset/autogen.sh: Update comment.
diff --git a/ChangeLog b/ChangeLog
index 62fd4ab..451374e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2026-03-26  Bruno Haible  <bruno@clisp.org>
+
+	Switch to autoconf 2.73.
+	* autogen.sh: Update comment.
+
 2026-03-06  Bruno Haible  <bruno@clisp.org>
 
 	Prepare for version 1.19.
diff --git a/autogen.sh b/autogen.sh
index 1109a28..c903f27 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -4,11 +4,11 @@
 # also regenerates all aclocal.m4, config.h.in, Makefile.in, configure files
 # with new versions of autoconf or automake.
 #
-# This script requires autoconf-2.63..2.72 and automake-1.11..1.18 in the PATH.
+# This script requires autoconf-2.63..2.73 and automake-1.11..1.18 in the PATH.
 # It also requires
 #   - the gperf program.
 
-# Copyright (C) 2003-2025 Free Software Foundation, Inc.
+# Copyright (C) 2003-2026 Free Software Foundation, Inc.
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
diff --git a/libcharset/ChangeLog b/libcharset/ChangeLog
index 5115d2b..98d3cb2 100644
--- a/libcharset/ChangeLog
+++ b/libcharset/ChangeLog
@@ -1,3 +1,8 @@
+2026-03-26  Bruno Haible  <bruno@clisp.org>
+
+	Switch to autoconf 2.73.
+	* autogen.sh: Update comment.
+
 2025-05-31  Bruno Haible  <bruno@clisp.org>
 
 	Switch to automake 1.18.
diff --git a/libcharset/autogen.sh b/libcharset/autogen.sh
index 45d0af4..d323309 100755
--- a/libcharset/autogen.sh
+++ b/libcharset/autogen.sh
@@ -2,9 +2,9 @@
 # Convenience script for regenerating all aclocal.m4, config.h.in, Makefile.in,
 # configure files with new versions of autoconf or automake.
 #
-# This script requires autoconf-2.63..2.71 and automake-1.11..1.18 in the PATH.
+# This script requires autoconf-2.63..2.73 and automake-1.11..1.18 in the PATH.
 
-# Copyright (C) 2003-2025 Free Software Foundation, Inc.
+# Copyright (C) 2003-2026 Free Software Foundation, Inc.
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by