Added mutalbe copy methods
Fixed a conflict
Added mutable copy method
Added MKNetworkOperation.serverTrustDelegate.

If set, this delegate will be called whenever a server presents an
SSL certificate that is not immediately trusted.  The delegate
can then make the trust decision (e.g. by asking the user).

The delegate must implement the new MKServerTrustDelegate protocol.
It has one method, handleServerCertificate.
Merge branch 'MKServerTrustDelegate'