Support writing classfile of version 52

Author: lrytz

src/compiler/scala/tools/nsc/backend/jvm/BCodeIdiomatic.scala

@@ -34,6 +34,7 @@ abstract class BCodeIdiomatic extends SubComponent {
     case "jvm-1.5"     => asm.Opcodes.V1_5
     case "jvm-1.6"     => asm.Opcodes.V1_6
     case "jvm-1.7"     => asm.Opcodes.V1_7
+    case "jvm-1.8"     => asm.Opcodes.V1_8
   }
 
   val majorVersion: Int = (classfileVersion & 0xFF)

src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala

@@ -381,6 +381,7 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
     case "jvm-1.5"     => asm.Opcodes.V1_5
     case "jvm-1.6"     => asm.Opcodes.V1_6
     case "jvm-1.7"     => asm.Opcodes.V1_7
+    case "jvm-1.8"     => asm.Opcodes.V1_8
   }
 
   private val majorVersion: Int = (classfileVersion & 0xFF)

src/compiler/scala/tools/nsc/settings/StandardScalaSettings.scala

@@ -39,7 +39,7 @@ trait StandardScalaSettings {
   val optimise:        BooleanSetting // depends on post hook which mutates other settings
   val print =          BooleanSetting ("-print", "Print program with Scala-specific features removed.")
   val target =          ChoiceSetting ("-target", "target", "Target platform for object files. All JVM 1.5 targets are deprecated.",
-                          List("jvm-1.5", "jvm-1.6", "jvm-1.7"), "jvm-1.6")
+                          List("jvm-1.5", "jvm-1.6", "jvm-1.7", "jvm-1.8"), "jvm-1.6")
   val unchecked =      BooleanSetting ("-unchecked", "Enable additional warnings where generated code depends on assumptions.")
   val uniqid =         BooleanSetting ("-uniqid", "Uniquely tag all identifiers in debugging output.")
   val usejavacp =      BooleanSetting ("-usejavacp", "Utilize the java.class.path in classpath resolution.")