`org-babel-result-end' bug fix and `org-babel-remove-result' regression tests.

* lisp/ob.el:

The code block below will currently act as though :results prepend 
is set. This is due to `org-babel-result-end' being unable to
find the correct end of a raw result. This patch fixes that.

#+begin_src emacs-lisp :results raw
"a line"
#+end_src

#+results:
a line
a line

* testing/lisp/test-ob.el:

Several regression tests that test the correct (multiple) execution of
code blocks in the various results formats. The tests also test that
'org-babel-remove-result' correctly removes the result.

Best, Martyn