The previous implementation would eagerly attempt TCP connection upon
receiving a DNS reply, but it would still wait for all the DNS results
before returning from the function.
This implementation returns immediately upon first successful TCP
connection, canceling not only in-flight TCP connection attempts but
also unfinished DNS queries.
Unfortunately this can't be implemented "above the vtable" because
various operating systems don't provide low level DNS resolution
primitives such as just putting the list of nameservers in a file.
Without libc on Linux it works great though!
Anyway this also changes the API to be based on Io.Queue. By using a
large enough buffer, reusable code can be written that does not require
concurrent, yet takes advantage of responding to DNS queries as they
come in. I sketched out a new implementation of `HostName.connect` to
demonstrate this, but it will require an additional API (`Io.Select`) to
be implemented in a future commit.
This commit also introduces "uncancelable" variants for mutex locking,
waiting on a condition, and putting items into a queue.
extract pure functional logic into pure functions and then layer the
scope crap on top properly
the formatting code incorrectly didn't do the reverse operation
(if_indextoname). fix that with some TODO panics
