sslutil: always use SSLContext
Now that we have a fake SSLContext instance, we can unify the code
paths for wrapping sockets to always use the SSLContext APIs.
Because this is security code, I've retained the try..except to
make the diff easier to read. It will be removed in the next patch.
I took the liberty of updating the inline docs about supported
protocols and how the constants work because this stuff is important
and needs to be explicitly documented.
(binary:application/octet-stream)