Skip EINTR errors on raw sockets

When system signal arrives to application locked on syscall - this syscall ends with EINTR error. Python convert such errors to different exceptions. Correct workaround - just run syscall again.

SSL sockets handles EINTR internally and application doesn't receive any exceptions. Raw sockets throws, and Sleek doesn't handle it correctly - it breaks current connection.

I've fixed at the most obvious and frequently executed syscalls.