Minor, improve exception message for reflection on built-ins

core/descriptors.runtime/src/org/jetbrains/kotlin/load/java/structure/reflect/ReflectJavaMember.kt

@@ -27,7 +27,7 @@ import java.lang.reflect.Type
 import java.util.*
 
 public abstract class ReflectJavaMember : ReflectJavaElement(), ReflectJavaAnnotationOwner, ReflectJavaModifierListOwner, JavaMember {
-    internal abstract val member: Member
+    public abstract val member: Member
 
     override val element: AnnotatedElement get() = member as AnnotatedElement
 

core/reflection.jvm/src/kotlin/reflect/jvm/internal/RuntimeTypeMapper.kt

@@ -131,7 +131,8 @@ internal object RuntimeTypeMapper {
                 }
                 // If it's a deserialized function but has no JVM signature, it must be from built-ins
                 return mapIntrinsicFunctionSignature(function) ?:
-                       throw KotlinReflectionInternalError("No metadata found for $function")
+                       throw KotlinReflectionInternalError("Reflection on built-in Kotlin types is not yet fully supported. " +
+                                                           "No metadata found for $function")
             }
             is JavaMethodDescriptor -> {
                 val method = ((function.source as? JavaSourceElement)?.javaElement as? ReflectJavaMethod)?.member ?: