Test demonstrating SI-8085

* The presentation compiler sourcepath is now correctly set-up.
* Amazingly enough (for me at least), the outer import in the
  package object seem to be responsible of the faulty behavior.
  In fact, if you move the import clause *inside* the package object,
  the test succeed!
  The test's output does provide the correct hint of this:

```
% diff /Users/mirco/Projects/ide/scala/test/files/presentation/t8085-presentation.log /Users/mirco/Projects/ide/scala/test/files/presentation/t8085.check
@@ -1,3 +1,2 @@
 reload: NodeScalaSuite.scala
-prefixes differ: <empty>.nodescala,nodescala
-value always is not a member of object scala.concurrent.Future
+Test OK
```

Notice the ``-prefixes differ: <empty>.nodescala,nodescala``. And compare
it with the output when the import clause is placed inside the package
object:

```
% diff /Users/mirco/Projects/ide/scala/test/files/presentation/t8085-presentation.log /Users/mirco/Projects/ide/scala/test/files/presentation/t8085.check
@@ -1,4 +1,2 @@
 reload: NodeScalaSuite.scala
-reload: NodeScalaSuite.scala
-open package module: package object nodescala
 Test OK
```

Notice now the ``-open package module: package object nodescala``!

Author: dotta

test/files/presentation/t8085.check

@@ -0,0 +1,3 @@
+reload: NodeScalaSuite.scala
+prefixes differ: <empty>.nodescala,nodescala
+value always is not a member of object scala.concurrent.Future

test/files/presentation/t8085.flags

@@ -0,0 +1 @@
+-sourcepath src

test/files/presentation/t8085/Test.scala

@@ -0,0 +1,28 @@
+import scala.tools.nsc.interactive.tests.InteractiveTest
+import scala.reflect.internal.util.SourceFile
+import scala.tools.nsc.interactive.Response
+
+object Test extends InteractiveTest {
+
+  override def execute(): Unit = {
+    // loadSourceAndWaitUntilTypechecked("package.scala") // <-- uncomment this line and the test succeed
+    val src = loadSourceAndWaitUntilTypechecked("NodeScalaSuite.scala")
+    checkErrors(src)
+  }
+
+  private def loadSourceAndWaitUntilTypechecked(sourceName: String): SourceFile = {
+    val sourceFile = sourceFiles.find(_.file.name == sourceName).head
+    askReload(List(sourceFile)).get
+    askLoadedTyped(sourceFile).get
+    sourceFile
+  }
+
+  private def checkErrors(source: SourceFile): Unit = compiler.getUnitOf(source) match {
+    case Some(unit) =>
+      val problems = unit.problems.toList
+      if(problems.isEmpty) reporter.println("Test OK")
+      else problems.foreach(problem => reporter.println(problem.msg))
+
+    case None => reporter.println("No compilation unit found for " + source.file.name)
+  }
+}

test/files/presentation/t8085/src/nodescala/Foo.scala

@@ -0,0 +1,3 @@
+package nodescala
+
+class Foo

test/files/presentation/t8085/src/nodescala/NodeScalaSuite.scala

@@ -0,0 +1,12 @@
+package nodescala
+
+import scala.concurrent.Future
+
+class NodeScalaSuite {
+  Future.always(517)
+
+  // This is here only to prove that the presentation compiler is instantiated with the
+  // correct `sourcepath` value (if it wasn't, you would see a `not found: type Foo` in
+  // the test's output
+  println(new Foo())
+}

test/files/presentation/t8085/src/nodescala/package.scala

@@ -0,0 +1,8 @@
+import scala.concurrent.Future // <-- if you move the import *inside* the package object, then it all works fine!!
+
+package object nodescala {
+  implicit class FutureCompanionOps[T](val f: Future.type) extends AnyVal {
+    def always[T](value: T): Future[T] = Promise[T].success(value).future
+  }
+}
+