Update the interpretation of --target-api.

Change-Id: I4ab158384d09470d84097d944ae1ddadeb2ad045
diff --git a/dx/src/com/android/dx/command/dexer/Main.java b/dx/src/com/android/dx/command/dexer/Main.java
index 16651a6..e810bca 100644
--- a/dx/src/com/android/dx/command/dexer/Main.java
+++ b/dx/src/com/android/dx/command/dexer/Main.java
@@ -1098,7 +1098,12 @@
             cfOptions.warn = DxConsole.err;
 
             dexOptions = new DexOptions();
-            dexOptions.enableExtendedOpcodes = targetApiLevel >= 12;
+
+            /*
+             * The new extended opcodes were introduced to the dex format
+             * as of API level 13 (aka Ice Cream Sandwich).
+             */
+            dexOptions.enableExtendedOpcodes = targetApiLevel >= 13;
         }
     }