* this changes into the ownCloud root directory and then should run just fine
* avoids weird error messages that are caused by this

The config directory must be taken from OC::$configDir

Minor fix

 - Remove uneeded slash in the configdir path.

In regard to a recent rant on social media where users complained about us to have broken the command line tool. Guess reading the documentation is hard…

Owncloud complains if the user runs a shell script with a user other than the user that owns `config/config.php`. The error message does not reflect this, and instead speaks about the web server user. Related issue: #15920 .

This reverts commit 6a1a4880.

Check for the posix extension - refs https://github.com/owncloud/core/pull/13282#issuecomment-69602645

This makes it still possible to update from the command line, but
disables custom commands from apps

switch structure enables many commands seamlessy.
also added some help and status command.