Merge pull request #593 from hintjens/master

Problem: ROUTER+RAW was not a clean API
Simplify ZMQ_STREAM socket implementation
Merge pull request #594 from hurtonm/master

Simplify ZMQ_STREAM socket implementation
Fixed zmq_errno function definition
Minor whitespace fixes in man page
Updated security mechanisms to use variable-length commands

RFC23, RFC24, RFC26 now use variable-length command names that
end in null octet (valid C strings) instead of fixed-length
space padded strings.