Try without identifying current user

Small change that warns the user if the current user cannot be identified rather than aborting.  This came in handy when I put dropbear on a dlink that did not have a true user environment.  Falling back on the "-l" option and user@ options works just fine as a client.  The only implication I found is that the -J option will fail ungracefully without a known own_user.
Merge pull request #2 from iquaba/patch-1

Try without identifying current user