[gtkmm] Auto-generate the ChangeLog from the git log for 'make dist'.

[José Alburquerque <jaalburqu src gnome org>]

commit f06d17901a55f0754234f52aab48463006bc4f67
Author: José Alburquerque <jaalburquerque gmail com>
Date:   Tue Jul 2 18:35:56 2013 -0400

    Auto-generate the ChangeLog from the git log for 'make dist'.
    
        * Makefile.am: Include the dist-changelog.am file copied in build/
        from mm-common so that the ChangeLog is automatically generated from
        the git commit messages on 'make dist'.

 Makefile.am |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 062ab2b..ffd75eb 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -58,3 +58,6 @@ dist_noinst_DATA = $(text_files) $(msvc_files) $(winstall_files)
 dist_noinst_SCRIPTS = autogen.sh
 
 DISTCLEANFILES = $(filter %mmconfig.h,$(msvc_files)) win32_installer/lgpl.txt
+
+# Optional: auto-generate the ChangeLog file from the git log on make dist
+include $(top_srcdir)/build/dist-changelog.am