Track whether global logging levels were set explicitly by the user or not.

main/command/src/main/scala/sbt/BasicKeys.scala

@@ -10,4 +10,5 @@ object BasicKeys
 	private[sbt] val interactive = AttributeKey[Boolean]("interactive", "True if commands are currently being entered from an interactive environment.", 10)
 	private[sbt] val classLoaderCache = AttributeKey[classpath.ClassLoaderCache]("class-loader-cache", "Caches class loaders based on the classpath entries and last modified times.", 10)
 	private[sbt] val OnFailureStack = AttributeKey[List[Option[String]]]("on-failure-stack", "Stack that remembers on-failure handlers.", 10)
+	private[sbt] val explicitGlobalLogLevels = AttributeKey[Boolean]("explicit-global-log-levels", "True if the global logging levels were explicitly set by the user.", 10)
 }

main/command/src/main/scala/sbt/State.scala

@@ -222,7 +222,7 @@ object State
 		def locked[T](file: File)(t: => T): T =
 			s.configuration.provider.scalaProvider.launcher.globalLock.apply(file, new Callable[T] { def call = t })
 
-		def interactive = s.get(BasicKeys.interactive).getOrElse(false)
+		def interactive = getBoolean(s, BasicKeys.interactive, false)
 		def setInteractive(i: Boolean) = s.put(BasicKeys.interactive, i)
 
 		def classLoaderCache: classpath.ClassLoaderCache = s get BasicKeys.classLoaderCache getOrElse newClassLoaderCache
@@ -247,4 +247,6 @@ object State
 		log.error(ErrorHandling reducedToString e)
 		log.error("Use 'last' for the full log.")
 	}
+	private[sbt] def getBoolean(s: State, key: AttributeKey[Boolean], default: Boolean): Boolean =
+		s.get(key) getOrElse default
 }

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

@@ -10,6 +10,7 @@ package sbt
 	import Def.ScopedKey
 	import Scope.GlobalScope
 	import MainLogging._
+	import BasicKeys.explicitGlobalLogLevels
 	import Keys.{logLevel, logManager, persistLogLevel, persistTraceLevel, state, traceLevel}
 	import scala.Console.{BLUE,RESET}
 
@@ -64,6 +65,11 @@ object LogManager
 		case Select(task) => ScopedKey(key.scope.copy(task = Global), task)
 		case _ => key // should never get here
 	}
+
+	private[this] def setExplicitGlobalLogLevels(s: State, flag: Boolean): State =
+		s.put(BasicKeys.explicitGlobalLogLevels, flag)
+	private[this] def hasExplicitGlobalLogLevels(s: State): Boolean =
+		State.getBoolean(s, BasicKeys.explicitGlobalLogLevels, default=false)
 }
 
 trait LogManager