Stops barking up the wrong tree with -Ywarn-dea...

Stops barking up the wrong tree with -Ywarn-dead-code. The origin of its
issues was twofold:

 1) synchronized acts by-name without being by-name (ticket #4086) 2)
 warnings are swallowed if context.reportGeneralErrors is false

Those two plus a dash of bitrot. In any case it's at its all time
happiest now. It found all the dead code related fixes in this commit.
Way to go, -Ywarn-dead-code! Review by odersky.

3 files changed, 3 insertions, 4 deletions

diff --git a/src/library/scala/io/BytePickle.scala b/src/library/scala/io/BytePickle.scala
index 3a51f2e0b8..97e3ff589d 100644
--- a/src/library/scala/io/BytePickle.scala
+++ b/src/library/scala/io/BytePickle.scala
@@ -144,7 +144,7 @@ object BytePickle {
         case Ref() =>
           val res2 = unat.appU(res._2)  // read location
           upe.get(res2._1) match {     // lookup value in unpickler env
-            case None => throw new IllegalArgumentException("invalid unpickler environment"); return null
+            case None => throw new IllegalArgumentException("invalid unpickler environment")
             case Some(v) => return (v.asInstanceOf[a], new UnPicklerState(res2._2, upe))
           }
       }
@@ -153,7 +153,7 @@ object BytePickle {
 
   def ulift[t](x: t): PU[t] = new PU[t] {
     def appP(a: t, state: Array[Byte]): Array[Byte] =
-      if (x != a) { throw new IllegalArgumentException("value to be pickled (" + a + ") != " + x); state }
+      if (x != a) throw new IllegalArgumentException("value to be pickled (" + a + ") != " + x)
       else state;
     def appU(state: Array[Byte]) = (x, state)
   }
diff --git a/src/library/scala/mobile/Code.scala b/src/library/scala/mobile/Code.scala
index 677248aabb..e1d04eafa5 100644
--- a/src/library/scala/mobile/Code.scala
+++ b/src/library/scala/mobile/Code.scala
@@ -197,7 +197,6 @@ class Code(clazz: java.lang.Class[_]) {
               cs(0).newInstance("").asInstanceOf[AnyRef]
             } else {
               system.error("class " + clazz.getName() + " has no public constructor")
-              null
             }
           }
         }
diff --git a/src/library/scala/xml/dtd/Scanner.scala b/src/library/scala/xml/dtd/Scanner.scala
index 0b2daa3284..1ac3c0f24d 100644
--- a/src/library/scala/xml/dtd/Scanner.scala
+++ b/src/library/scala/xml/dtd/Scanner.scala
@@ -65,7 +65,7 @@ class Scanner extends Tokens with parsing.TokenTests {
       case ENDCH => END
       case _     =>
         if (isNameStart(c)) name; // NAME
-        else { system.error("unexpected character:"+c); END }
+        else system.error("unexpected character:" + c)
     }
 
   final def name = {