Don't concatenate in a loop

[daurnimator]

You should never append to a lua string in a loop: add elements to a table then use table.concat.

Seen @ https://github.com/icgood/ratchet/blob/master/src/zmq.c#L372

[daurnimator]

Also found: https://github.com/icgood/ratchet/blob/master/src/http/common.lua#L19 https://github.com/icgood/ratchet/blob/master/src/http/client.lua#L27 https://github.com/icgood/ratchet/blob/master/src/http/client.lua#L72 https://github.com/icgood/ratchet/blob/master/src/http/server.lua#L26 https://github.com/icgood/ratchet/blob/master/src/http/server.lua#L133

https://github.com/icgood/ratchet/blob/master/src/smtp/client.lua#L101 https://github.com/icgood/ratchet/blob/master/src/smtp/common.lua#L83 https://github.com/icgood/ratchet/blob/master/src/smtp/common.lua#L462

https://github.com/icgood/ratchet/blob/master/src/socketpad/init.lua#L146