SSL: session id context now includes certificate hash.

This prevents inappropriate session reuse in unrelated server{}
blocks, while preserving ability to restore sessions on other servers
when using TLS Session Tickets.

Additionally, session context is now set even if there is no session cache
configured.  This is needed as it's also used for TLS Session Tickets.

Thanks to Antoine Delignat-Lavaud and Piotr Sikora.
Updated OpenSSL used for win32 builds.