A double goodness whammy involving type inferen...

A double goodness whammy involving type inference at the borders.

1) Implicit search preserves singleton type fidelity. 2) Unification of
parent bounds is (closer to) correct.

Result of 1: "implicit def f(x: Foo.type)" will convert object Foo.
Result of 2: "new Trait[Int] { }" may enjoy its type constructor being
inferred, no longer foiled by the anonymous class.

Also included are some clarity-enhnancing renamings and refactorings.
Performance note: I heavily benchmarked the change to isSubArgs and it
is reproducibly faster than the previous implementation. Numbers and
methodology available upon request.

Closes #2693, #3964. Review by moors, who wrote most of this patch but
might like to review the comments.

1 files changed, 6 insertions, 0 deletions

diff --git a/test/files/pos/bug2693.scala b/test/files/pos/bug2693.scala
new file mode 100644
index 0000000000..97732cf081
--- /dev/null
+++ b/test/files/pos/bug2693.scala
@@ -0,0 +1,6 @@
+class A {
+  trait T[A]
+  def usetHk[T[_], A](ta: T[A]) = 0
+  usetHk(new T[Int]{}: T[Int])
+  usetHk(new T[Int]{}) // fails with: found: java.lang.Object with T[Int], required: ?T[ ?A ]
+}
\ No newline at end of file