One of the test cases currently aborts when using gcc's flag -ftrapv, due to
negating an INT64_MIN int64 variable, which is an undefined operation.
This will be fixed in a subsequent commit.
CBigNum::setint64() does 'n <<= 8', where n is of type "long long".
This leads to shifting onto and past the sign bit, which is undefined
behavior in C++11 and can cause problems in the future.
This prevents an undefined operation in main.cpp, when shifting the hash value
left by 32 bits.
Shifting a signed int left into the sign bit is undefined in C++11.
Ricardo M. Correia