Added GenTraversableLike.ungroupBy
Added Stream.cond
File.children & File.tree can now handle unreadable directories
Merge branch 'master' into 2.9

Conflicts:
	core/src/main/scala/pimpathon/list.scala
	core/src/main/scala/pimpathon/set.scala
	core/src/test/scala/pimpathon/util.scala