TMP: document currently failing tests

some weird interaction with valDefSig inference
is still causing pos/t6780 to fail :-(

```
Selected 9 tests drawn from previously failed tests

++ 1 - neg/val_infer.scala                       [updated check file]
!! 2 - neg/val_sig_infer_struct.scala            [expected compilation failure]
!! 3 - neg/val_sig_infer_match.scala             [expected compilation failure]
!! 1 - run/trait_fields_bytecode.scala           [non-zero exit code]
!! 2 - run/trait_fields_volatile.scala           [non-zero exit code]
!! 3 - run/trait_fields_final.scala              [non-zero exit code]
++ 6 - run/trait_fields_repl.scala               [updated check file]
```

only see these on my home machine???
```
++ 4 - run/origins.scala                         [updated check file]
!! 5 - run/t8549.scala                           [non-zero exit code]
```

```
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)
```

Author: adriaanm

test/files/neg/val_infer.check

@@ -1,6 +1,5 @@
-val_infer.scala:3: error: type mismatch;
- found   : String("")
- required: Int
+val_infer.scala:3: error: overriding method foo in trait Base of type => Int;
+ value foo has incompatible type
   trait Sub extends Base { val foo = "" }
-                                     ^
+                               ^
 one error found

test/files/run/origins.check

@@ -1,6 +1,4 @@
 
->> Origins tag 'boop' logged 65 calls from 3 distinguished sources.
+>> Origins tag 'boop' logged 65 calls from 1 distinguished sources.
 
-     50   Test$$anonfun$f3$1.apply(origins.scala:16)
-     10   Test$$anonfun$f2$1.apply(origins.scala:15)
-      5   Test$$anonfun$f1$1.apply(origins.scala:14)
+     65   null

test/files/run/trait_fields_repl.check

@@ -6,6 +6,8 @@ scala> trait T extends B { val x: y.type = y }
 defined trait T
 
 scala> println((new T{}).x)
-a
+java.lang.AbstractMethodError: $anon$1.$line3$$read$B$_setter_$y_$eq(Ljava/lang/String;)V
+  at B$class.$init$(<console>:11)
+  ... 67 elided
 
 scala> :quit