Report getaddrinfo() failure result in Socket.error and error_str (not errno)

As Nelgin pointed out, a Socket.connect() failure for reasons of address/host
lookup failure would report a stale/nonsense Socket.error/error_str value.

This change required us to query/store the socket API/getaddrinfo error string
at the time of failure (for the Socket.error_str property value) rather than
converting from number to string at the time the property is read.

This does mean that sometimes Socket.error is a errno value and sometimes its
a getaddrinfo (EAI_*) error value. Since the EAI_* values are negative, it
should be obvious which is which.