Generate ChangeLog from git log during 'make dist'

Generate the ChangeLog using git log in the dist-hook target of the main
Makefile.  The git command used is:

	git log --stat --name-only --date=iso

The format of the resulting ChangeLog is different to the old one that
was produced with cvs2cl.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>

Makefile.am

@@ -16,6 +16,20 @@ ACLOCAL_AMFLAGS = -I m4
 DISTCHECK_CONFIGURE_FLAGS = RUBY_PREFIX='$${prefix}' --disable-ruby-binding
 
 dist-hook:
+	@if test -d "$(srcdir)/.git"; \
+	then \
+		echo Creating ChangeLog && \
+		( cd "$(top_srcdir)" && \
+		  echo '# Generated by Makefile.  Do not edit.'; echo; \
+		  $(top_srcdir)/missing --run \
+		  git log --stat --name-only --date=iso ) \
+		 > ChangeLog.tmp \
+		&& mv -f ChangeLog.tmp $(distdir)/ChangeLog \
+		|| ( rm -f ChangeLog.tmp ; \
+		     echo Failed to generate ChangeLog >&2 ); \
+	else \
+		echo A git clone is required to generate a ChangeLog >&2; \
+	fi
 
 dev:
 	-for i in `seq 0 15`; do \