This is basically the same as
package scala.util.parsing.combinator.syntactical
import scala.util.parsing._
import scala.util.parsing.combinator._
...
So by “stacking” the packages the way you wrote you can get super-packages in scope. See also these answers.
[Update] Here is a new article written by Martin Odersky about this topic: http://www.artima.com/scalazine/articles/chained_package_clauses_in_scala.html