Redis Add QUIT to command table, remove HOST: and POST

Some people complain that QUIT is missing from help / command table, and instead there's a hack in processCommand with a comment that i don't understand.

At the same time, HOST: and POST are there in the command table although these are not real commands. They would appear in the COMMAND command, and even in commandstats. what's worse, since HOST: contains :, it used to mess up the INFO parsing until we added getSafeInfoString