A number of corrections of the aep engine implementation:

1. rnd_reference was a duplication of the work the the engine
   framework does, and wasn't ever checked.  Removed.
2. use the NO_ macros to disable appropriate algorithms.
3. Only implement the RNG stuff if AEPRAND is defined (default: not
   defined, because the AEP people plan on having boards without it.
   I'll see if I can device a more dynamic way of disabling this).
4. aep_finish() now closes all connections, and if that worked, does a
   proper finalize.
5. proper AEP types are used to conform to the AEP definitions of
   their own functions.
6. remake the use of thread locks.  The use of CRYPTO_LOCK_DYNLOCK was
   definitely inappropriate, and for random generator stuff, it's
   better to use CRYPTO_LOCK_RAND.

Also, I applied certain changes that were provided by the AEP people.
Among others, BN_CTX_new() is not used to initialise a BN context
(this was never done before, and may have made things slower or not
working at all.