Fixes https://github.com/owncloud/core/issues/16560

drop any fallback code related to curl - refs https://github.com/owncloud/core/pull/14838#issuecomment-78586447

This reverts commit 6a1a4880.

Beside some small improvements and bug fixes this will probably the final state for OC8.

To test this you need to set up two ownCloud instances. Let's say:

URL: myPC/firstOwnCloud user: user1
URL: myPC/secondOwnCloud user: user2
Now user1 can share a file with user2 by entering the username and the URL to the second ownCloud to the share-drop-down, in this case "user2@myPC/secondOwnCloud".

The next time user2 login he will get a notification that he received a server-to-server share with the option to accept/decline it. If he accept it the share will be mounted. In both cases a event will be send back to user1 and add a notification to the activity stream that the share was accepted/declined.

If user1 decides to unshare the file again from user2 the share will automatically be removed from the second ownCloud server and user2 will see a notification in his activity stream that user1@myPC/firstOwnCloud has unshared the file/folder from him.

Both are removed from 5.4.0

Safe Mode: http://php.net/manual/en/features.safe-mode.php
> This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 5.4.0.

Magic Quotes: http://php.net/manual/en/security.magicquotes.php
> This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 5.4.0.

We do not want to follow redirects to other protocols since they might allow an adversary to bypass network restrictions. (i.e. a redirect to ftp:// might be used to access files of a FTP server which might be in a secure zone and not be reachable from the net but from the ownCloud server)

Get final redirect manually using get_headers()

Migrate to HTTPHelper class and add unit tests