This obviates custom code to emulate a thread-safe connection.
Use this for testing that listeners close if the connection breaks.
R=dave, agl, fullung
CC=golang-dev
https://golang.org/cl/11781043
* Remove special handling for dynamically allocated
ports. This was a bug in OpenSSH 5.x sshd.
* Run the test with a preselected port number.
* Run TestPortForward only on unix platforms.
R=dave, agl
CC=golang-dev
https://golang.org/cl/10049045