The sendto() interface as defined in Python documentation:
socket.sendto(string, address)
socket.sendto(string, flags, address)
I didn't catch the fact that [1] broke this, this patch fixes it and add
a sendto/recvfrom test to make sure it doesn't happen again (turns out
we didn't have any).
GitHub issue: https://github.com/eventlet/eventlet/issues/290
Fixes: bc4d1b5 - gh-274: Handle blocking I/O errors in GreenSocket
[1] bc4d1b5d36