MAJOR: cli: Use a custom .snd_buf function to only copy the current c…

…ommand

The CLI applet is now using its own snd_buf callback function. Instead of
copying as most output data as possible, only one command is copied at a
time.

To do so, a new state CLI_ST_PARSEREQ is added for the CLI applet. In this
state, the CLI I/O handle knows a full command was copied into its input
buffer and it must parse this command to evaluate it.

include/haproxy/cli-t.h

@@ -56,6 +56,7 @@ enum {
 	CLI_ST_INIT = 0,   /* initial state, must leave to zero ! */
 	CLI_ST_END,        /* final state, let's close */
 	CLI_ST_GETREQ,     /* wait for a request */
+	CLI_ST_PARSEREQ,   /* pase a request */
 	CLI_ST_OUTPUT,     /* all states after this one are responses */
 	CLI_ST_PROMPT,     /* display the prompt (first output, same code) */
 	CLI_ST_PRINT,      /* display const message in cli->msg */