[asm-cherry-pick] asm.CustomAttribute class

Allows creating an asm.Attribute and directly providing the content
as a byte array.

Cherry-pick of f994343. Only `CustomAttr.java` is kept, the file
`SignatureChecker.java` has been removed in f9053e5.

Author: magarciaEPFL

src/asm/scala/tools/asm/CustomAttr.java

@@ -0,0 +1,20 @@
+/* NSC -- new Scala compiler
+ * Copyright 2005-2012 LAMP/EPFL
+ */
+
+package scala.tools.asm;
+
+import scala.tools.asm.Attribute;
+
+/**
+ * A subclass of ASM's Attribute for the sole purpose of accessing a protected field there.
+ *
+ */
+public class CustomAttr extends Attribute {
+
+    public CustomAttr(final String type, final byte[] value) {
+        super(type);
+        super.value = value;
+    }
+
+}