Polished for the official review, addressing several TODOs.

Polished for the official review, addressing several TODOs.

Use 1.1 version for FTP ports because FTP commands are sent on a
"persistent by default" connection, just like HTTP/1.1.

Cleaned up Ftp::CtrlChannel, Ftp::DataChannel, and Ftp::Client object
construction and destruction.

Do not insist on USER command when intercepting FTP. Interception support
may still not work for other reasons, but USER does not seem to be required
since Squid gets request destination from the intercepted connection info.