Multifile class part names are "1${PartName}".

Multifile class parts are final.

compiler/backend/src/org/jetbrains/kotlin/codegen/MultifileClassPartCodegen.kt

@@ -47,7 +47,7 @@ public class MultifileClassPartCodegen(
 ) : MemberCodegen<JetFile>(state, null, partContext, file, v){
     override fun generateDeclaration() {
         v.defineClass(element, Opcodes.V1_6,
-                      Opcodes.ACC_SYNTHETIC,
+                      Opcodes.ACC_FINAL,
                       filePartType.internalName,
                       null,
                       "java/lang/Object",

compiler/frontend.java/src/org/jetbrains/kotlin/fileClasses/JvmFileClassUtil.kt

@@ -56,7 +56,7 @@ public object JvmFileClassUtil {
             file.packageFqName.child(Name.identifier(manglePartName(jvmFileClassAnnotations.name, file.name)))
 
     public @JvmStatic fun manglePartName(facadeName: String, fileName: String): String =
-            "${facadeName}__${PackagePartClassUtils.getFilePartShortName(fileName)}"
+            "1${PackagePartClassUtils.getFilePartShortName(fileName)}"
 
     public @JvmStatic fun parseJvmFileClass(annotations: Annotations): ParsedJmvFileClassAnnotations? {
         val jvmName = annotations.findAnnotation(JVM_NAME) ?: return null