Wrap test calls with `(eval-after-load "ert-autoloads"...)

Following issue #2 and PR #3

All tests are ok:

```sh

$ make test
emacs -Q --batch -l ert -l *.el -f ert-run-tests-batch-and-exit
Running 4 tests (2014-11-01 13:25:27+0100)
passed  1/4  org-toc-test-flush-subheadings
passed  2/4  org-toc-test-hrefify-gh
passed  3/4  org-toc-test-hrefify-toc
passed  4/4  org-toc-test-raw-toc

Ran 4 tests, 4 results as expected (2014-11-01 13:25:27+0100)

```
(Note: I did not add the Makefile this time :D)

Cheers,