Automatically generate ChangeLog when building dist

Automatically generate ChangeLog when building distributions using
'git log'.

.gitignore

@@ -9,6 +9,7 @@
 Makefile
 Makefile.in
 Makefile.in.in
+glabels-*.tar.gz
 
 #
 # Explicit files and patterns

Makefile.am

@@ -32,3 +32,16 @@ DISTCLEANFILES = gnome-doc-utils.make
 
 DISTCHECK_CONFIGURE_FLAGS = --disable-scrollkeeper
 
+dist-hook:
+	@if test -d "$(srcdir)/.git"; \
+	then \
+		echo Creating ChangeLog && \
+		(GIT_DIR=$(top_srcdir)/.git \
+		  ./missing --run git log -M -C --name-status --date=short --no-color) | \
+		  fmt --split-only > 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