SI-7507 Fix lookup of private[this] member in presence of self type.

In the following code:

	trait Cake extends Slice

	trait Slice { self: Cake =>    // must have self type that extends `Slice`
	  private[this] val bippy = () // must be private[this]
	  locally(bippy)
	}

`ThisType(<Slice>)`.findMember(bippy)` excluded the private local member on
the grounds that the first class in the base type sequence, `Cake`, was
not contained in `Slice`.

	scala> val thisType = typeOf[Slice].typeSymbol.thisType
	thisType: $r.intp.global.Type = Slice.this.type

	scala> thisType.baseClasses
	res6: List[$r.intp.global.Symbol] = List(trait Cake, trait Slice, class Object, class Any)

This commit changes `findMember` to use the symbol of the `ThisType`, rather
than the first base class, as the location of the selection.

2 files changed, 11 insertions, 0 deletions

diff --git a/test/files/neg/t7507.check b/test/files/neg/t7507.check
new file mode 100644
index 0000000000..d402869fd4
--- /dev/null
+++ b/test/files/neg/t7507.check
@@ -0,0 +1,4 @@
+t7507.scala:6: error: value bippy in trait Cake cannot be accessed in Cake
+  locally(bippy)
+          ^
+one error found
diff --git a/test/files/neg/t7507.scala b/test/files/neg/t7507.scala
new file mode 100644
index 0000000000..1b4756d955
--- /dev/null
+++ b/test/files/neg/t7507.scala
@@ -0,0 +1,7 @@
+trait Cake extends Slice {
+  private[this] val bippy = ()
+}
+
+trait Slice { self: Cake =>
+  locally(bippy)
+}