FSMTimingSpec overhaul

- revise timings to make them more robust (granularity changed in
  general from 100ms to 500ms)
- make one test more deterministic by awaiting context.hasMessages,
  which has been added for this purpose; is the same kind of “non-racy”
  as isShutdown
- add static version of TestKit.awaitCond (checked that it does not
  conflict, even when “import TestKit._” is used; seems like imports are
  not even searched if the symbol is found locally)

akka-testkit/src/main/scala/akka/testkit/TestKit.scala

@@ -555,6 +555,36 @@ class TestKit(_app: AkkaApplication) {
 
 object TestKit {
   private[testkit] val testActorId = new AtomicInteger(0)
+
+  /**
+   * Block until the given condition evaluates to `true` or the timeout
+   * expires, whichever comes first.
+   *
+   * If no timeout is given, take it from the innermost enclosing `within`
+   * block.
+   *
+   * Note that the timeout is scaled using Duration.timeFactor.
+   */
+  def awaitCond(p: ⇒ Boolean, max: Duration, interval: Duration = 100.millis) {
+    val stop = now + max
+
+    @tailrec
+    def poll(t: Duration) {
+      if (!p) {
+        assert(now < stop, "timeout " + max + " expired")
+        Thread.sleep(t.toMillis)
+        poll((stop - now) min interval)
+      }
+    }
+
+    poll(max min interval)
+  }
+
+  /**
+   * Obtain current timestamp as Duration for relative measurements (using System.nanoTime).
+   */
+  def now: Duration = System.nanoTime().nanos
+
 }
 
 /**