Add FindBugs to Travis CI (closes #262)

This patch copies the FindBugs configuration in pom.xml from the
reporting section to the build section so findbugs can be used as part
of the build process (by using the maven goal findbugs:check).

It then adds this goal to the Travis CI build so that FindBugs
becomes part of the CI, and new patches would be prevented from
introducing new FindBugs errors.

.travis.yml

@@ -22,7 +22,7 @@ jdk:
   - oraclejdk8
 
 script:
-  - mvn test apache-rat:check clirr:check checkstyle:check javadoc:javadoc -B
+  - mvn test apache-rat:check clirr:check checkstyle:check findbugs:check javadoc:javadoc -B
 
 after_success:
   - mvn clean cobertura:cobertura coveralls:report

pom.xml

@@ -660,6 +660,15 @@
           <enableRulesSummary>false</enableRulesSummary>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>findbugs-maven-plugin</artifactId>
+        <!-- Use version from parent pom as that is adjusted according to the Java version used to run Maven -->
+        <version>${commons.findbugs.version}</version>
+        <configuration>
+          <excludeFilterFile>${basedir}/findbugs-exclude-filter.xml</excludeFilterFile>
+        </configuration>
+      </plugin>
     </plugins>
 
   </build>