Rewrote Clause::Subsumes(), Clause::PropagateUnit[s]().

Using explicit for loops instead of std::[any|all]_of().
For Clause::Subsumes(), this reduces the average performance to n+m
instead of n*m.

For short clauses as we usually have them the performance gain is
minimal. It might be substantial however for the new
Clause::PropagateUnits(), which could be used when Setup manages the
unit clauses in a sorted set structure.

Also moved Literal::Complementary() and Literal::Subsumes() back to
readable versions. It seems the compiler optimises these expressions
to some expression with the same performance as the bitwise
expressions.