public Expression getOriginalExpression() {
    return originalExpression;
  }
Used to represent the argument to Specification.old() once it has been processed
by IRewriteResources.captureOldValue(). The original expression is
kept in case ConditionRewriter still needs it.

@author Peter Niederwieser
spock-core/src/main/java/org/spockframework/compiler/OldValueExpression.java