Remove call to acquire_credentials.

Remove the "gss.acquire_credentials" call, which a) should never be needed, and b) will sometimes fail.

This call was failing in my environment, and to the best of my knowledge, even if it succeeds, the credentials it acquires will never be used. The default usage for acquire_credentials, if none is specified, is "acceptor". However, acceptor credentials at the GSS layer are never used by init_sec_context.
Always forward Kerberos tickets.

Adding ":delegate => true" to the init_context call causes Kerberos tickets to be forwarded to the remote host.  This may or may not be a good idea.

Pro: This is consistent with the behavior of the gem under ruby1.8.

Con: This might be a security issue, and tickets should really only be forwarded if the user specifies that this is what they want.

It wasn't immediately obvious to me how to make this optional, so I'm submitting this the "dumb" version of this change with the above caveats.
Merge pull request #1 from ljulien/master

Remove acquire_credentials and use delegation to forward tickets.