Bye-bye ReflectiveAccess, introducing PropertyMaster, see #1750

- PropertyMaster is the only place in Akka which calls
  ClassLoader.getClass (apart from kernel, which might be special)
- all PropertyMaster methods (there are only three) take a ClassManifest
  of what is to be constructed, and they verify that the obtained object
  is actually compatible with the required type

Other stuff:
- noticed that I had forgotten to change to ExtendedActorSystem when
  constructing Extensions by ExtensionKey (damn you, reflection!)
- moved Serializer.currentSystem into JavaSerializer, because that’s the
  only one needing it (it’s only used in readResolve() methods)
- Serializers are constructed now with one-arg constructor taking
  ExtendedActorSystem (if that exists, otherwise no-arg as before), to
  allow JavaSerializer to do its magic; possibly necessary for others as
  well
- Removed all Option[ClassLoader] signatures
- made it so that the ActorSystem will try context class loader, then
  the class loader which loaded the class actually calling into
  ActorSystem.apply, then the loader which loaded ActorSystemImpl
- for the second of the above I added a (reflectively accessed hopefully
  safe) facility for getting caller Class[_] objects by using
  sun.reflect.Reflection; this is optional an defaults to None, e.g. on
  Android, which means that getting the caller’s classloader is done on
  a best effort basis (there’s nothing we can do because a StackTrace
  does not contain actual Class[_] objects).
- refactored DurableMailbox to contain the owner val and use that
  instead of declaring that in all subclasses

akka-remote/src/main/scala/akka/serialization/ProtobufSerializer.scala

@@ -5,6 +5,7 @@
 package akka.serialization
 
 import com.google.protobuf.Message
+import akka.actor.PropertyMaster
 
 /**
  * This Serializer serializes `com.google.protobuf.Message`s
@@ -19,7 +20,7 @@ class ProtobufSerializer extends Serializer {
     case _          ⇒ throw new IllegalArgumentException("Can't serialize a non-protobuf message using protobuf [" + obj + "]")
   }
 
-  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]], classLoader: Option[ClassLoader] = None): AnyRef =
+  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]]): AnyRef =
     clazz match {
       case None    ⇒ throw new IllegalArgumentException("Need a protobuf message class to be able to serialize bytes using protobuf")
       case Some(c) ⇒ c.getDeclaredMethod("parseFrom", ARRAY_OF_BYTE_ARRAY: _*).invoke(null, bytes).asInstanceOf[Message]