[dasher] Make PACKAGE_URL work with all versions of autoconf. (#615564)

[Patrick Welche <pwelche src gnome org>]

commit 9026e56b95f1d3acd99c977af723f2cb3c658041
Author: Patrick Welche <prlw1 cam ac uk>
Date:   Wed Apr 14 18:22:26 2010 +0100

    Make PACKAGE_URL work with all versions of autoconf. (#615564)

 ChangeLog    |    2 ++
 configure.ac |   13 ++++++++-----
 2 files changed, 10 insertions(+), 5 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 58b139d..55190c9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,8 @@
 2010-04-14  Patrick Welche <prlw1 cam ac uk>
 
 	* dasher.xml.in: Save Christian Kirbach's typo corrections.
+	* configure.ac: Make PACKAGE_URL work with all versions of autoconf.
+	  (#615564)
 
 2010-04-12  Patrick Welche <prlw1 cam ac uk>
 
diff --git a/configure.ac b/configure.ac
index 8887b5c..5aca74f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2,13 +2,16 @@ AC_PREREQ(2.59)
 AC_INIT([dasher],
   m4_esyscmd([build-aux/mkversion]),
   [http://bugzilla.gnome.org/enter_bug.cgi?product=dasher],
-  [dasher])
+  [dasher],
+  [http://www.inference.phy.cam.ac.uk/dasher/])
 
 # This becomes part of AC_INIT in autoconf 2.64
-PACKAGE_URL="http://www.inference.phy.cam.ac.uk/dasher/";
-AC_DEFINE_UNQUOTED([PACKAGE_URL], ["$PACKAGE_URL"],
-                   [Define to the home page for this package.])
-AC_SUBST([PACKAGE_URL])
+m4_ifndef([AC_PACKAGE_URL],
+	[m4_define([AC_PACKAGE_URL],[http://www.inference.phy.cam.ac.uk/dasher/])
+	AC_DEFINE_UNQUOTED([PACKAGE_URL],
+                       [AC_PACKAGE_URL],
+                       [Define to the home page for this package.])
+	AC_SUBST([PACKAGE_URL],[AC_PACKAGE_URL])])
 
 AC_CONFIG_SRCDIR([Src/main.cc])
 AC_CONFIG_HEADERS(config.h)