Also:
- Move deadline check from createStream() into SocketStream().
- Get rid of unused code in an old attempt by me to refactor createStream().
- Fix inverted check > 0 vs < 0 on one of the 2 usleep()s to back-off connect() in SocketStream().
- Move EndOfStreamException and TimeOutException out of their classes (and fix up users).
- Replace readdir() by readdir_r(). Probably irrel since only retval checked vs 0.
- Clarify ~FileDescriptorBasedStream() somewhat, only delay cancellation if actually calling close().
- Constify a few local vars in SocketStream.cc.

Reason: In APERTIF, we need to receive UDP frames from the FPGA correlator.
We can live with LOFAR Common and Stream, but prefer not to have CoInterface just for createStream().
(All other network communication will be done via QPID messaging middleware.)

Build tested only.