* _check_resolved_address() is implemented with getaddrinfo() which is slow
* If available, use socket.inet_pton() instead of socket.getaddrinfo(), because
  it is much faster

Microbenchmark (timeit) on Fedora 21 (Python 3.4, Linux 3.17, glibc 2.20) to
validate the IPV4 address "127.0.0.1" or the IPv6 address "::1":

* getaddrinfo() 10.4 usec per loop
* inet_pton(): 0.285 usec per loop

On glibc older than 2.14, getaddrinfo() always requests the list of all local
IP addresses to the kernel (using a NETLINK socket). getaddrinfo() has other
known issues, it's better to avoid it when it is possible.

Just try to be consistent: _debug was already used in some places, and always
used in BaseProactorEventLoop.

Don't use yield/yield-from in an except block of a generator. Store the
exception and handle it outside the except block.

Close the transport, not directly the pipe.

Kill the process on timeout: don't keep a running process in the backgroud!

transport was closed. The check broken a Tulip example and this limitation is
arbitrary. Check if _proc is None should be enough.

Enhance also close(): do nothing when called the second time.