Clean-up: remove `is_null` throughout the code base.
Clean-up: replace `sizeof()` by `count()`.
Remove ancient argument documentation for site-ssh.
Merge pull request #475 from damz/pr/cleanups/6.x

Clean-up the code base (6.x) getting rid of is_null().
Fix unish_file_delete_recursive() out of sync with drush_delete_dir()
Fix drush_find_tmp() variable

Seems its using a wrong variable to check if the directory exists or not
Add 'copy' download type to copy existing folders from repo
Adding download copy docs and example [ci skip]
Added error message if site-set command can't create temp file.
Added missing simpletest dependency to test-run command.
Updated documentation for drush_log.

  Provide a few more details about 'ok', so it's a more obvious alternative to
  drush_print, when developers want to print messages to screen and log.

	modified:   drush.inc
By mpdonadio: force result-file=FALSE for _drush_sql_get_db_table_list().
resolving symlinks in drush shell script fails if path contains spaces
Fix "Undefined index: time in queue.drush.inc."
Merge pull request #534 from TravisCarden/queue-cron-time-6

Follow-up to #515 to backport to 6.x
Fix #526. _drush_sitealias_site_list() searches too many files. Slows down bash completion.
oops - really limit _drush_sitealias_site_list() to 1 subdir.
Follow-up to #530: Fix broken multi-user support in `site-set` command.
Update command 'category' element when it gets remapped. Only affects JSON/var_export of help command.
Really delete temp files with suffixes.