Initialize cipher context in KRB5
("D. Russell" <russelld@aol.net>)

Allow HMAC functions to use an alternative ENGINE.

sure they are available in opensslconf.h, by giving them names starting
with "OPENSSL_" to avoid conflicts with other packages and by making
sure e_os2.h will cover all platform-specific cases together with
opensslconf.h.

I've checked fairly well that nothing breaks with this (apart from
external software that will adapt if they have used something like
NO_KRB5), but I can't guarantee it completely, so a review of this
change would be a good thing.

"Jan Mikkelsen" <janm@transactionsite.com> correctly states that the
OpenSSL header files have #include's and extern "C"'s in an incorrect
order.  Thusly fixed.

structure and decides what key to generate (if any). Not currently added to
the PBE algorithm list because it is largely untested.

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Reviewed by:
PR: