Build: Omit pre-5.0.0 entries from the generated ChangeLog.

It makes ChangeLog significantly smaller.
diff --git a/Makefile.am b/Makefile.am
index 1053697..16db514 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -77,7 +77,8 @@
 # Convert the man pages to PDF and plain text (ASCII only) formats.
 dist-hook:
 	if test -d "$(srcdir)/.git" && type git > /dev/null 2>&1; then \
-		( cd "$(srcdir)" && git log --date=iso --stat ) \
+		( cd "$(srcdir)" && git log --date=iso --stat \
+			b667a3ef6338a2c1db7b7706b1f6c99ea392221c^..HEAD ) \
 			> "$(distdir)/ChangeLog"; \
 	fi
 	if type groff > /dev/null 2>&1 && type ps2pdf > /dev/null 2>&1; then \