Autogenerate the ChangeLog from git history

Moved the old ChangeLog out of the way. Place instructions in
a placeholder ChangeLog.

Makefile.am

@@ -68,5 +68,22 @@ DISTCHECK_CONFIGURE_FLAGS = \
     --disable-update-mime-database \
     --enable-gtk-doc
     
+CHANGELOG_START = \
+	d2f8367dc600080b6cf3edbe4e2fc204f929471e
+
+dist-hook:
+	@if test -d "$(srcdir)/.git"; \
+	then \
+		echo Creating ChangeLog && \
+		( cd "$(top_srcdir)" && \
+		  echo '# Generate automatically. Do not edit.'; echo; \
+		  $(top_srcdir)/missing --run git log $(CHANGELOG_START).. --stat --date=short ) > ChangeLog.tmp \
+		&& mv -f ChangeLog.tmp $(top_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
+
 distuninstallcheck:
 	@: