Prototypes and constant declarations for non-copying reads and writes for
BIO pairs (which is totally untested as of now, so I don't yet commit
the actual source code, but reserve the numbers to avoid conflicts).

and make it the default for some debugging configurations.

with cc (but not gcc) seems to work well with BN_LLONG; but -O4 is too
much.

"Zot O'Connor" <zot@ZotConsulting.com>).
Also, Windows probably does not need the warning about multi-threading.

(problems with BN_LLONG have been reported both for hpux-cc
and for hpux10-gcc).

Submitted by: Andreas Ley <andy@rz.uni-karlsruhe.de