Make release tarballs friendlier to older tar versions

git-tar-tree adds an extended pax header to archives if its first
parameter points to a commit.  It confuses older tars and isn't
very useful in the case of git anyway, so stop doing it.

Idea: Junio, implementation: Junio.  I just wrote it up. :-)

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -667,7 +667,7 @@ git.spec: git.spec.in
 
 GIT_TARNAME=git-$(GIT_VERSION)
 dist: git.spec git-tar-tree
-	./git-tar-tree HEAD $(GIT_TARNAME) > $(GIT_TARNAME).tar
+	./git-tar-tree HEAD^{tree} $(GIT_TARNAME) > $(GIT_TARNAME).tar
 	@mkdir -p $(GIT_TARNAME)
 	@cp git.spec $(GIT_TARNAME)
 	@echo $(GIT_VERSION) > $(GIT_TARNAME)/version