Fix memory leak

Using a lazy val causes the log manager to hold onto a reference to the
state. These would accumulate with each task evaluation. I found that
that in the beanpuree project, that if I ran compile 10 times in a row,
the heap usage was 40mb lower after this change.

main/src/main/scala/sbt/internal/LogManager.scala

@@ -174,7 +174,7 @@ object LogManager {
       key: ScopedKey[_],
       state: State
   ): SuppressedTraceContext => Option[String] = {
-    lazy val display = Project.showContextKey(state)
+    val display = Project.showContextKey(state)
     def commandBase = "last " + display.show(unwrapStreamsKey(key))
     def command(useFormat: Boolean) =
       if (useFormat) BLUE + commandBase + RESET else s"'$commandBase'"