Instead of positively implying the negative sink type, negative sink characteristics now negatively imply all sink types (but not source types). This is simpler and sice we will never have a huge number of sink types it doesn't impact performance either.
Changes to test results:
- The call to `createDirectories` at `Test.java:87` is now correctly classified as a source candidate, having previously been erroneously excluded by a negative _sink_ characteristic.
- The call to `compareTo` at `Test.java:48` is now erroneously classified as a source candidate; it should be suppressed by `IsSanitizerCharacteristic`, which is a negative sink characteristic, but should really be a negative source characteristic.
- In framework mode, several endpoints are now erroneously classified as source candidates even though they have neutral models, because `NeutralModelCharacteristic` is currently only a negative sink characteristic and not a negative source characteristic.
