Add Checkstyle CovariantEquals

Author: garydgregory

src/conf/checkstyle.xml

@@ -50,6 +50,7 @@ limitations under the License.
   <module name="TreeWalker">
     <module name="ArrayTypeStyle" />
     <module name="AvoidStarImport" />
+    <module name="CovariantEquals" />
     <module name="ExplicitInitializationCheck" />
     <module name="FinalLocalVariable" />
     <module name="IllegalImport" />