Remove 'regsiter' keyword

C++11 deprecated the 'register' keyword. C++17, removes the 'register' keyword.

details here: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0001r1.html

So NTpsec needs to remove all uses of the 'register' keyword. A quick scan shows about a fw dozen places to be changed.