Add test for explicit ordering
Use Ordering/ComparisonChain in ValidationThread
Update to Guava 18
Split LintRuleComparator into Lint{Rule,Error}Orderings

- Add tests for LintErrorOrderings, LintRuleOrderings
Use Ordering rather than manual Comparators
Add toString implementations for LintRule, ProgramOptions
Add @Nullable, and ignore FindBug's complaints
Print Exception summary if available
Prevent initialization of EnumUtils
Update CHANGELOG
Improve tests for Reporters