Drop test that lower bound must be a subtype of upper bound.

As discussed in #780 and #525, the test is not needed. This makes
t1279a compile, which got moved now to pos. Fixes #780 and #915.
It also makes scala.List compile. Review by @smarter.

Author: odersky

src/dotty/tools/dotc/typer/Typer.scala

@@ -864,8 +864,6 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val TypeBoundsTree(lo, hi) = desugar.typeBoundsTree(tree)
     val lo1 = typed(lo)
     val hi1 = typed(hi)
-    if (!(lo1.tpe <:< hi1.tpe))
-      ctx.error(d"lower bound ${lo1.tpe} does not conform to upper bound ${hi1.tpe}", tree.pos)
     assignType(cpy.TypeBoundsTree(tree)(lo1, hi1), lo1, hi1)
   }
 

test/dotc/scala-collections.whitelist

@@ -112,8 +112,7 @@
 ./scala-scala/src/library/scala/collection/immutable/Iterable.scala
 ./scala-scala/src/library/scala/collection/immutable/LinearSeq.scala
 
-# https://github.com/lampepfl/dotty/issues/915
-# ./scala-scala/src/library/scala/collection/immutable/List.scala
+./scala-scala/src/library/scala/collection/immutable/List.scala
 ./scala-scala/src/library/scala/collection/immutable/MapProxy.scala
 ./scala-scala/src/library/scala/collection/immutable/PagedSeq.scala
 ./scala-scala/src/library/scala/collection/immutable/Queue.scala

tests/pos/bounds.scala

@@ -9,3 +9,10 @@ object ListMap {
   def empty[X, Y] = new ListMap[X, Y]
   def apply[A1, B2](elems: Tuple2[A1, B2]*): Map[A1, B2] = empty[A1,B2].++(elems.iterator)
 }
+
+class Test[A] {
+
+  def f[B >: A <: AnyRef](x: A): AnyRef = (x: B)
+  def g[B >: String <: Int](x: B): Int = x
+
+}