Clean-up: remove `is_null` throughout the code base.
Clean-up: replace `sizeof()` by `count()`.
Remove ancient argument documentation for site-ssh.
Remove drupal_mapp_assoc(), follow change notice https://drupal.org/node/2207453
Merge pull request #491 from andypost/master

Issue-490 Remove drupal_map_assoc()
Merge pull request #474 from damz/pr/cleanups/master

Clean-up the code base (master), getting rid of is_null().
Fix unish_file_delete_recursive() out of sync with drush_delete_dir().
Try to fix test failures.