Add --src/dst-prefix to git-formt-patch in git-rebase.sh

For the case of "diff.noprefix" in git-config, git-format-patch should
still output diff with standard prefixes for git-am

Signed-off-by: Oded Shimon <ods15@ods15.dyndns.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -544,6 +544,7 @@ fi
 if test -z "$do_merge"
 then
 	git format-patch -k --stdout --full-index --ignore-if-in-upstream \
+		--src-prefix=a/ --dst-prefix=b/ \
 		--no-renames $root_flag "$revisions" |
 	git am $git_am_opt --rebasing --resolvemsg="$RESOLVEMSG" &&
 	move_to_original_branch