[libsigc++2] Auto-generate the ChangeLog from the git log for 'make dist'.

[José Alburquerque <jaalburqu src gnome org>]

commit 7c62df6ee76e21a16f3b836f5d21cbdb3a9688b9
Author: José Alburquerque <jaalburquerque gmail com>
Date:   Tue Jul 2 17:40:57 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 8b157ca..98bd10f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -43,3 +43,6 @@ dist_noinst_DATA = $(addprefix MSVC_Net2005/,$(msvc_net2005_data)) \
 
 DISTCLEANFILES = MSVC_Net2005/sigc++config.h MSVC_Net2008/sigc++config.h \
                  MSVC_Net2010/sigc++config.h
+
+# Optional: auto-generate the ChangeLog file from the git log on make dist
+include $(top_srcdir)/build/dist-changelog.am