Improved message for missing argument list

Clarifies the language and rules for eta-expansion.

A missing argument in a list, as opposed to a missing
argument list, results in a different message.

The comical expansion in parens does not attempt to show
what was already applied, but succeeds in showing at a
glance the shape of the method in question.

```
scala> def m(i: Int, j: Int)(x: Int) = ???
m: (i: Int, j: Int)(x: Int)Nothing

scala> m
<console>:12: error: missing argument list for method m
Unapplied methods are only converted to functions when a function type is expected.
You can make this conversion explicit by writing `m _` or `m(_,_)(_)` instead of `m`.
       m
       ^
```

The original submission was due to sschaef and the wording due
to adriaanm, with a minor tweak.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/files/neg/missing-arg-list.scala b/test/files/neg/missing-arg-list.scala
new file mode 100644
index 0000000000..c422dd32fe
--- /dev/null
+++ b/test/files/neg/missing-arg-list.scala
@@ -0,0 +1,13 @@
+
+trait T {
+
+  def id(i: Int) = i
+  def f(i: Int)(j: Int) = i+j
+  def g(i: Int, j: Int, k: Int) = i+j+k
+  def h(i: Int, j: Int, k: Int)(implicit s: String) = s*(i+j+k)
+
+  val w = id
+  val x = f
+  val y = g
+  val z = h
+}