* lisp/ob-tangle.el (org-babel-tangle-collect-blocks): Preserver order
of code blocks from the source document.
* testing/lisp/test-ob-tangle.el (ob-tangle/block-order): New test.
Reported-by: Kaushal Modi <kaushal.modi@gmail.com>
<http://lists.gnu.org/r/emacs-orgmode/2018-10/msg00062.html>