Minor, add toString() to OutputFile for debugging

compiler/backend-common/src/output.kt

@@ -33,6 +33,8 @@ public trait OutputFile {
     public val sourceFiles: List<File>
     public fun asByteArray(): ByteArray
     public fun asText(): String
+
+    override fun toString() = "$relativePath (compiled from $sourceFiles)"
 }
 
 class SimpleOutputFile(

compiler/backend/src/org/jetbrains/jet/codegen/ClassFileFactory.java

@@ -80,6 +80,7 @@ public final class ClassFileFactory extends GenerationStateAware implements Outp
         }
     }
 
+    @NotNull
     @Override
     public List<OutputFile> asList() {
         done();
@@ -173,11 +174,13 @@ public final class ClassFileFactory extends GenerationStateAware implements Outp
             this.relativeClassFilePath = relativeClassFilePath;
         }
 
+        @NotNull
         @Override
         public String getRelativePath() {
             return relativeClassFilePath;
         }
 
+        @NotNull
         @Override
         public List<File> getSourceFiles() {
             ClassBuilderAndSourceFileList pair = generators.get(relativeClassFilePath);
@@ -210,6 +213,12 @@ public final class ClassFileFactory extends GenerationStateAware implements Outp
         public String asText() {
             return builderFactory.asText(generators.get(relativeClassFilePath).classBuilder);
         }
+
+        @NotNull
+        @Override
+        public String toString() {
+            return getRelativePath() + " (compiled from " + getSourceFiles() + ")";
+        }
     }
 
     private static final class ClassBuilderAndSourceFileList {