Experimental task progress interface. Fixes #592.

Set sbt.task.timings=true to print timings for tasks.
This sample progress handler shows how to get names for tasks and
deal with flatMapped tasks.  There are still some tasks that make
it through as anonymous, which needs to be investigated.

A setting to provide a custom handler should come in a subsequent commit.

util/collection/src/main/scala/sbt/IDSet.scala

@@ -12,6 +12,7 @@ trait IDSet[T]
 	def ++=(t: Iterable[T]): Unit
 	def -= (t: T): Boolean
 	def all: collection.Iterable[T]
+	def toList: List[T]
 	def isEmpty: Boolean
 	def foreach(f: T => Unit): Unit
 	def process[S](t: T)(ifSeen: S)(ifNew: => S): S
@@ -38,6 +39,7 @@ object IDSet
 		def ++=(t: Iterable[T]) = t foreach +=
 		def -= (t:T) = if(backing.remove(t) eq null) false else true
 		def all = collection.JavaConversions.collectionAsScalaIterable(backing.keySet)
+		def toList = all.toList
 		def isEmpty = backing.isEmpty
 		def process[S](t: T)(ifSeen: S)(ifNew: => S) = if(contains(t)) ifSeen else { this += t ; ifNew }
 		override def toString = backing.toString