Append port to trusted domain in case it's not 80 or 443

See https://github.com/owncloud/core/pull/10584#issuecomment-54677059 for reference.

@ronnicek Can you please test this change? Thanks.

\cc @MTRichards FYI. 
This is in `init()`, `init` is called differently from `handleRequest()` (see https://github.com/owncloud/core/blob/c79c894dbb6bda06ff32db4418b8fe6af5b27d4a/index.php#L26 which includes base.php which in turns calls init)

So we have to exit() in init or move `handleRequest` at the end of init. What would you prefer?