BUG/MINOR: cli: Report an error to user if command or payload is too big

BUG/MINOR: cli: Report an error to user if command or payload is too big

Too big command, larger than a buffer, was silently rejected by the CLI
applet. It was handled as an error and the connection was closed, but no
error message was reported to user to notify him. Now an error is reported
before closing. It is only displayed if the chunk buffer used by the CLI
applet is full and no delimiter (\n or ;) is found to mark the end of the
command. It works for a simple command but also for a command with a huge
payload.

This patch could be backported to all stable versions.