Fixed a bug where "0UL > 0xfffffffffffff000UL" evaluated to true, because the large unsigned long value overflowed the (signed) java long the computation was done in. Other parts of the AbstractExpressionValueVisitor seem a bit fishy, too, though, and there may be more bugs like this one. We should think about using BigInteger (and probably also BigDecimal) more consequently to prevent these issues.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13757 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c