Ability to alter element created by media_token_to_markup()

for the testbot

We'll need to have this applied to 7.x-2.x first, and also documented in media.api.php.

media_filter_alter_hook.patch queued for re-testing.

I had a use for this in a project so I gave this a review and it seems handy to have for now. Here's a revised patch including some documentation and re-rolled for the current code.

Note that the original patch had:
drupal_alter('media_token_to_markup', $element, $file, $tag_info);

And this has:
drupal_alter('media_token_to_markup', $element, $tag_info, $settings);

This is because it's important that we pass along $settings to the alter hooks (since we'd want to be able to check $settings['wysiwyg']), and since drupal_alter() is limited to three parameters, we included $file in $tag_info['file'] instead.

#6 has been committed to both branches:
http://drupalcode.org/project/media.git/commit/0ad4d7a
http://drupalcode.org/project/media.git/commit/cd8db74