webdav returns "503 Service Unavailable" in case the ownCloud server is currently in maintenance mode.

This means that OC_Connector_Sabre_Client is no longer needed

Only show the version updating to instead of worrying about converting internal to a formatted version

Special case of BSD has been added as stat syntax differs
In addition unknown OS is logged

And some documentation adjusted on the way

Fall back to default log file if logfile config file not found, suppress writing errors, fixes issue #826

getUrlContent should take proxy setting into consideration when not using curl, as well

Thanks Bart for the hint.
This also switches "==" to "<>" and not the code actually works ;-)

https://github.com/owncloud/core/issues/504