for background on the new socket option NN_RCVMAXSIZE, here's the original planning discussion: http://www.freelists.org/post/nanomsg/issue-with-received-message-size,1

and from the nn_setsockopt() documentation:

NN_RCVMAXSIZE
Maximum message size that can be received, in bytes. Negative value means that the received size is limited only by available addressable memory. The type of this option is int. Default is 1024kB.

let's add a prototype method rcvmaxsize() like the rest of sockopt API.

anyone sending msgs larger than the default will find this useful, to avoid unexpected close/disconnect