C++17 fixes

[chruffins]

This pull request fixes an issue where SBSAT does not compile for C++17 or later because sbsat_headers.h uses using namespace std;, and do_prover3.cc declares a global variable int size which is implicitly std::size, and std::size is already defined in the standard library for C++17.

Also, I added a fix for compiler warnings for BOOL_MAX and removed the register keyword from all *.cc files as it does nothing in C++17.