Fine-tuning contexts for resolve overloading

When resolving overloading with a fun proto type, we need to evaluate the arguments in the current context, not in an exploring context. Reason: The argument types might contain type valiables that are constrained in the context and that needs to be maintained.

Author: odersky

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

@@ -1150,7 +1150,7 @@ class Typer extends Namer with Applications with Implicits {
       val alts = altDenots map (alt =>
         TermRef.withSig(ref.prefix, ref.name, alt.info.signature, alt))
       def expectedStr = err.expectedTypeStr(pt)
-      resolveOverloaded(alts, pt)(ctx.fresh.withExploreTyperState) match {
+      resolveOverloaded(alts, pt) match {
         case alt :: Nil =>
           adapt(tree.withType(alt), pt)
         case Nil =>