build: don't include merges into changelog

Makefile.am

@@ -17,7 +17,7 @@ ChangeLog: __force-changelog-generation
 		for tag in $$(git tag | $(EGREP) '^[0-9]+(\.[0-9]+){1,}$$' | sort -t. -k 1,1nr -k 2,2nr -k 3,3nr); do \
 			if [ x"$$prev" = x ]; then prev=$$tag ; fi ; \
 			if [ x"$$prev" = x"$$tag" ]; then continue; fi ; \
-			echo "$$prev [$$(git log $$prev -1 --pretty=format:'%ai')]:" ; \
+			echo "$$prev [$$(git log --no-merges $$prev -1 --pretty=format:'%ai')]:" ; \
 			echo "" ; \
 			git log --pretty=' - [%h] %s (%an)' $$tag..$$prev ; \
 			echo "" ; \