net/http: Transport.CloseIdleConnections doesn't close idle http2 connections

[bradfitz]

The http.Transport is wired up with a hidden http2.Transport by default.

But http.Transport.CloseIdleConnections doesn't call the same method on the hidden http2 transport.

[gopherbot]

CL https://golang.org/cl/18679 mentions this issue.

[gopherbot]

CL https://golang.org/cl/18678 mentions this issue.