Enable unbind and disconnect methods for class socket only for ZMQ >= 3.2
Merge pull request #52 from xdmiodz/develop

Enable unbind and disconnect methods for class socket only for ZMQ >= 3.2
zmqpp::socket::receive_raw also has int length

As with my previous pull request for send_raw, the buffer for receive_raw has an
int for length rather than a size_t. I added unit tests for testing sending >2GB
messages using zmqpp::socket and now something fails inside ZMQ. It returns with
EAGAIN.
Merge pull request #53 from cmdevries/develop

zmqpp::socket::receive_raw also has int length
Flags are ignored on signal receive overload.
Merge pull request #55 from pschoeni/patch-1

Flags are ignored on signal receive overload.
Revert "Flags are ignored on signal receive overload."
Merge pull request #56 from pschoeni/revert-55-patch-1

Revert "Flags are ignored on signal receive overload."