SMP SSL session cache implementation

SMP SSL session cache implementation

This patch implement SSL session cache sharing across SMP workers using shared
memory. The following new squid configuration options added:

 - The "sslproxy_session_cache_size" option which sets the cache size to use
   for ssl session. Example usage:
     sslproxy_session_cache_size 4 MB

 - The "sslproxy_session_ttl" option which defines the time in seconds the
   ssl session is valid. Example usage:
     sslproxy_session_ttl  600

This is a Measurement Factory project