net/http: TestServerExpect is broken on windows-amd64

<pre>C:\src\pkg\net\http&gt;http.test.exe -test.v -test.run=Expect -test.timeout=5s
=== RUN TestServerExpect
panic: test timed out

goroutine 18 [running]:
testing.alarm()
        /root/go/root/src/pkg/testing/testing.go:463 +0x4a
created by time.goFunc
        /root/go/root/src/pkg/time/sleep.go:94 +0x4b
...

Also see windows-amd64 go builder at rev ad78acd6f0bb.

Alex</pre>
