Exception thrown on recv if survey timed out

[daniel-j-h]

Submitting this as an issue, otherwise it gets lost on the mailinglist:
http://www.freelists.org/post/nanomsg/cppnanomsg-throws-on-recv-if-survey-timed-out

• recv throws except for EAGAIN
• should also allow error codes such as ETIMEDOUT, EFSM

The wrapper is not usable for the survey pattern, as it returns EFSM right now (should be ETIMEDOUT, see: nanomsg/nanomsg#194).

There's only a single exception type. Catching it on deadline expiration may also catch a fatal error.
There's no way to distinguish between them.