net: don't prefer IPv4 addresses during resolution

Currently the address resolution family defaults to IPv4. Instead remove
the preference and instead resolve to a family suitable for the host.

Expose the getaddrinfo flags and allow them to be passed.

Add documentation about new flags.

Reviewed-by: Trevor Norris <trev.norris@gmail.com>
dns: fix GetAddrInfo assert

The method GetAddrInfo() is used by more than just dns.lookup(), and in
those cases a third argument isn't passed. This caused the following
check to abort:

  assert(args[3]->IsInt32());

Fixes: 4306786 "net: don't prefer IPv4 addresses during resolution"

Signed-off-by: Trevor Norris <trev.norris@gmail.com>
fs: fs.readFile should not throw uncaughtException

Reviewed-By: Fedor Indutny <fedor@indutny.com>