net: delete TestDialTimeoutHandleLeak

It is too flaky. Tried to make it more reliable,
but that affects other tests (they run too long),
because we do unusual things here, like attempting
to connect to non-existing address and interrupt.

R=golang-dev, bradfitz, mikioh.mikioh
CC=golang-dev
https://codereview.appspot.com/7314097
mime: use .wav instead of .bmp during windows tests

Some systems do not have .bmp mime.

Update issue 4723.

R=golang-dev, bradfitz, dave
CC=golang-dev
https://codereview.appspot.com/7326047