[Owncloud] Add shared reverse SSL-proxy support

[Stefan Herbrechtsmeier]

Hi,

I have updated and reworked the shared reverse SSL-proxy support 
(https://ssl-proxy.com/domain.tld/) (see merge request #74 / Bug report 
oc-890, oc-1161) to minimize the influence to other proxy configuration:
- Add WEBROOT to form action in login.php template
- Replace $_SERVER['REQUEST_URI'] with new OC_Helper::requestUri function
- Replace 3rdparty changes with Sabre_HTTP_Request connector (subclass)
- Replace SSL-proxy forward detection with host name compare
- Make SSL-proxy url configurable

I have upload the changes to 
https://gitorious.org/~herbrechtsmeier/owncloud/herbrechtsmeiers-owncloud/commits/sslproxy.

It would be nice if a reverse SSL-proxy support could be added to 
owncloud and I am willing to help.

Regards,
     Stefan