Warnings with scala.xml refs in Scaladoc

Adding the following to your `build.sbt`, 

```scala
autoAPIMappings := true

libraryDependencies +=
  "org.scala-lang.modules" %% "scala-xml" % "1.2.0"
```

Running `doc` in sbt produces the following warnings if you cross-reference anything in scala.xml:

    Could not find any member to link for "scala.xml.Node".

