Change the EVP_somecipher() and EVP_somedigest()
functions to return constant EVP_MD and EVP_CIPHER
pointers.

Update docs.

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.

Remove duplicated code in EVP.

Second phase of EVP cipher overhaul.

Change functions like EVP_EncryptUpdate() so they now return a
value. These normally have software only implementations
which cannot fail so this was acceptable. However ciphers
can be implemented in hardware and these could return errors.

Beginnings of EVP cipher overhaul. This should eventually
enhance and tidy up the EVP interface.

This patch adds initial support for variable length ciphers
and changes S/MIME code to use this.

Some other library functions need modifying to support use
of modified cipher parameters.

Also need to change all the cipher functions that should
return error codes, but currenly don't.

And of course it needs extensive testing...

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Reviewed by:
PR: