Backport javadoc config changes from 3.0.

Author: olim7t

pom.xml

@@ -192,18 +192,39 @@
         <artifactId>maven-javadoc-plugin</artifactId>
         <version>2.9.1</version>
         <configuration>
+          <verbose>false</verbose>
+          <additionalparam>${javadoc.opts}</additionalparam>
           <!-- I can haz math in my javadoc (see http://zverovich.net/2012/01/14/beautiful-math-in-javadoc.html) -->
-          <additionalparam>-header '&lt;script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"&gt;&lt;/script&gt;'</additionalparam>
+          <header>
+            &lt;script type="text/javascript"
+            src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"&gt;&lt;/script&gt;
+          </header>
+          <!-- open external links in a separate window -->
+          <bottom>
+            &lt;script type="text/javascript"&gt;
+            for(var i in document.links) {
+            var link = document.links[i];
+            if (link.href.indexOf('is-external=true') != -1) link.target = '_blank';
+            }
+            &lt;/script&gt;
+          </bottom>
+          <links>
+            <link>https://docs.oracle.com/javase/8/docs/api/</link>
+            <link>http://docs.guava-libraries.googlecode.com/git-history/v16.0.1/javadoc/</link>
+            <link>http://netty.io/4.0/api/</link>
+            <!-- dependencies from driver-extras -->
+            <link>http://www.joda.org/joda-time/apidocs/</link>
+            <link>http://fasterxml.github.io/jackson-core/javadoc/2.6/</link>
+            <link>http://fasterxml.github.io/jackson-databind/javadoc/2.6/</link>
+            <link>https://javaee-spec.java.net/nonav/javadocs/</link>
+          </links>
         </configuration>
         <executions>
           <execution>
             <id>attach-javadocs</id>
             <goals>
               <goal>jar</goal>
             </goals>
-            <configuration>
-              <additionalparam>${javadoc.opts}</additionalparam>
-            </configuration>
           </execution>
         </executions>
       </plugin>