getaddrinfo, freeaddrinfo, getnameinfo support

It's probably helpful to look at both commits separately.

The first commit tweaks the new ipv6 functionality added by https://github.com/kripken/emscripten/pull/1348 so that the internal functions (inet_ntop4, inet_pton4, etc.) are prefixed with an underscore. Further, inet_ntop6_raw was changed to take in an array of integers as opposed to a pointer to the heap. `inet_ntoa_raw` was renamed to be `inet_ntop4_raw` to be consistent with `inet_ntop6_raw`. The `test_inet*` and `test_getaddrinfo` tests were moved into the sockets test suite. And finally, `test_sockets_getaddrinfo` was re-enabled and consolidated with `test_getaddrinfo`.

The second commit adds support for `getaddrinfo`, `freeaddrinfo` and `getnameinfo`. Part of that meant moving some of the fake IP generation / resolution code that previously existed in `gethostbyname` into the two new internal functions `_lookup_name` and `_lookup_addr`. Tests were added for all of them.

Ran all of the socket tests and o1 and other just to be safe.