bpo-27340: Use memoryview in SSLSocket.sendall() (#3384)

* bpo-27340: Use memoryview in SSLSocket.sendall()

SSLSocket.sendall() now uses memoryview to create slices of data. This fix
support for all bytes-like object. It is also more efficient and avoids
costly copies.

Signed-off-by: Christian Heimes <christian@python.org>

* Cast view to bytes, fix typo

Signed-off-by: Christian Heimes <christian@python.org>