only pass stdin to hijack when needed
Merge pull request #2399 from dotcloud/fix_race_stdin_cli

Only pass stdin to hijack when needed
Removes \\n from debugf calls
Merge pull request #2400 from dotcloud/remove_newline_debugf

Removes \n from debugf calls
Clarified the documentation for the -p flag.

It was unclear to me that you could pass in a host port.