Sort howto documents in howto-index.txt

Howto documents in howto-index.txt were listed in a rather
random order. So better sort them.

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -309,7 +309,7 @@ $(patsubst %.txt,%.texi,$(MAN_TXT)): %.texi : %.xml
 
 howto-index.txt: howto-index.sh $(wildcard howto/*.txt)
 	$(QUIET_GEN)$(RM) $@+ $@ && \
-	'$(SHELL_PATH_SQ)' ./howto-index.sh $(wildcard howto/*.txt) >$@+ && \
+	'$(SHELL_PATH_SQ)' ./howto-index.sh $(sort $(wildcard howto/*.txt)) >$@+ && \
 	mv $@+ $@
 
 $(patsubst %,%.html,$(ARTICLES)) : %.html : %.txt