This improves performance using 512bit SIMD instructions.

Fixes #4115.

It looks like older versions of GCC have slightly unreliable logic for array out-of-bounds detection.
Code in ethash which uses unions and arrays is firing a warning in both Debian Jesse (8.5) and in the ARM Linux cross-builds.
Debian Jesse uses GCC 4.9.2.   The cross-builds are using GCC 4.8.4.
Other distros are using GCC 5.x or even GCC 6.x (Arch).
The issue is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56273 and was fixed in GCC 5.0 and backported to 4.9.3.

Updated comments.

With this change we will be able to remove a global warning suppression from our CMake files.

 * Add the ProgPow code for client
 * fix a mem crash, which results from light is NULL in full node mode. So I pass blocknumber from EthashAux to ethash_full_compute and ethash_hash
 * misunderstanding mix and result before. fix

 * and support progpow_light_compute()
 * remove duplication codes.
 * fixed misc bugs.
 * See also:
   - chfast/ethash#108
   - ethereum/go-ethereum#17731
   - https://github.com/ifdefelse/cpp-ethereum/tree/a998c9e9335f4f8bfc89a4f9598d1cce8fad3330

based on "EIP-1057 algorithm clarifications"
ethereum/EIPs#1618

 * unique sources for random math by ifdefelse - ifdefelse/ProgPOW@824cd79
 * test cases from : chfast/ethash#116 by chfast

temporally fixed golang wrapper