x/crypto/ssh/terminal: have MakeRaw mirror cfmakeraw.
x/crypto/ssh/terminal: have MakeRaw mirror cfmakeraw.

Rather than guessing at which terminal flags should be set or cleared by
MakeRaw, this change tries to make it mirror the behaviour documented
for cfmakeraw() in the termios(3) manpage.

Fixes golang/go#15625

Change-Id: Icd6b18ffb57ea332147c8c9b25eac5e41eb0863a
Reviewed-on: https://go-review.googlesource.com/22964
Run-TryBot: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Faiyaz Ahmed <ac06fd84eefddccf0728b64df0d68a10f8f3fb5e@vmware.com>
Reviewed-by: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

golang/term