At the same time, add VMS support for Rijndael.

comment out in the previous commit

and for small 'a' also a couple of calls to
BN_mod_mul_montgomery(r, r, r, ...).

BN_mod_exp_atalla could be used.

BN_mod_exp. Call the regular atalla mod_exp operation instead.

marginally faster BN_mod_exp for 1024 bit exponents.

because we're only handling words anyway) in BN_mod_exp_mont_word
making it a little faster for very small exponents,
and adjust the performance gain estimate in CHANGES according
to slightly more thorough measurements.
(15% faster than BN_mod_exp_mont for "large" base,
20% faster than BN_mod_exp_mont for small base.)

temporary BIGNUMs. BN_CTX still uses a fixed number of BIGNUMs, but
the BN_CTX implementation could now easily be changed.

but the BN code had some problems that would cause failures when
doing certificate verification and some other functions.

Submitted by: Eric A Young from a C2Net version of SSLeay
Reviewed by: Mark J Cox
PR: