minor tweak, avoid some work if banned client arrives
don't flag error if we are to send a further response.
fix up error return values on socket for win32

not sure if my update to mingw has changed some assumptions or whether there was a
some mismatch with some DLLs but in certain cases sockets were reporting error codes
that did not match expectations (EINTR vs WSAEINTR etc, typical MS).  This broke
certain things like auth checks and probably a bunch of others.

Same codebase has been working in previous builds so better to define this more
completely.
expand on previous patch, avoid messages in error log
minor log message change