platforms.

PR: 1667

So in a sense this commit reverts few latest ones fixing bugs in original
code and improving it, most notably adding 64-bit support [though not in
BN_nist_mod_224 yet].
PR: 1593

PR: 1593

PR:1664

PR: 1609

PR: 1552
Submitted by: Roumen Petrov <openssl@roumenpetrov.info>

PR: 1607
Submitted by: "Christophe Macé" <mace.christophe@gmail.com>

PR: 1659

PR: 1552
Submitted by: Roumen Petrov <openssl@roumenpetrov.info>, "Alon Bar-Lev" <alon.barlev@gmail.com>

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