recv returns false if first message frame gives EINTR
handle either completion or returning false on EINTR depending on frame
treat EINTR as timeout during poll
Merge pull request #34 from benjamg/feature/cleanly_handle_eintr

Feature/cleanly handle eintr
"make clean" should get rid of all builds, not just the active one.
Created a variadic add() function on zmqpp::message_t, and a variadic constructor which delegates to it. Also created a variadic extract() function for retreiving values. Although get() would have been more consistent with the existing interface, a variadic get() was not compatible with the existing methods.
Merge pull request #36 from LindleyF/develop

Develop
Better handling of EINTR in send_raw, receive_raw, receive(string),
and context::terminate. Also cause ~context to call terminate() which was
not previously occurring.

Also added reinterpret_casts to ensure the variadic message::add() method
was not called when the low-level void* overload was intended.
added missing header & fixed initializer warnings
Merge pull request #37 from TobiasSimon/develop

added missing header & fixed initializer warnings
Merge branch 'develop' of https://github.com/zeromq/zmqpp into develop
Merge pull request #38 from LindleyF/develop

Develop
Merge branch 'develop' of github.com:zeromq/zmqpp into develop