Faster timeout when connecting

Use non-blocking connects, and a select() call to wait a predefined
time (5s by default, but configurable with -timeout) for either
success or failure. This allows much more connections to be tried
per time unit.

Based on a patch by phantomcircuit.

src/util.h

@@ -105,6 +105,8 @@ T* alignup(T* p)
 typedef int socklen_t;
 #else
 #define WSAGetLastError()   errno
+#define WSAEINVAL           EINVAL
+#define WSAEALREADY         EALREADY
 #define WSAEWOULDBLOCK      EWOULDBLOCK
 #define WSAEMSGSIZE         EMSGSIZE
 #define WSAEINTR            EINTR