implement getsockname, getpeername, and getaddrinfo

[dicej]

This also includes stubs for gethostbyname, gethostbyaddr, etc. which were necessary to get CPython to build. I believe it will be possible to implement them all properly at some point, but don't have the bandwidth at the moment.

Finally, this includes a few fixes for issues I missed in earlier PRs that surfaced when running the CPython asyncio test suite.

[abrown]

Looking at this again, did we mean to expose the tcp|udp_get* functions as defined symbols (e.g., tcp_getpeername)? cc: @dicej

[dicej]

@abrown It depends on what you mean by "expose". Everything's exposed due to -fvisibility=default here and will presumably remain that way until we start annotating deliberately-exported functions with explicit visibility (at which point we can stop using -fvisibility=default). Those functions aren't in any public header file, though, so they're not exposed in that sense AFAIK.