Note changes re: session ID generation callbacks, etc.

 Changes between 0.9.6 and 0.9.7  [xx XXX 2000]

  *) Add support for overriding the generation of SSL/TLS session IDs.

     These callbacks can be registered either in an SSL_CTX or per SSL.

     The purpose of this is to allow applications to control, if they wish,

     the arbitrary values chosen for use as session IDs, particularly as it

     can be useful for session caching in multiple-server environments. A

     command-line switch for testing this (and any client code that wishes

     to use such a feature) has been added to "s_server".

     [Geoff Thorpe, Lutz Jaenicke]

  *) Modify mkdef.pl to recognise and parse prprocessor conditionals

     of the form '#if defined(...) || defined(...) || ...' and

     '#if !defined(...) && !defined(...) && ...'.  This also avoids