Messages implicitly converted to string

[platy]

Background I have just spent a lot of time debugging an issue of an array containing a single buffer being sent to ZMQ - in my test cases it worked but with production data there were extra bytes appearing all over the place.

Problem The OutBuffer silently converts things which are not buffers into strings - link The String conversion for arrays converts each element to string and concatenates them, the String conversion for Buffer treats the buffer as containing a UTF-8 encoded string. So for most cases you don't notice a problem like this - ~60% of bytes are valid and survive.

Proposal I don't think doing this conversion is worth the trouble it can cause - I think we should throw a TypeError - I will send a PR.