implement EnclosingMethod attribute for local classes

implement the new EnclosingMethod attribute described in the latest JSR202 draft:

The EnclosingMethod Attribute
 
The EnclosingMethod attribute is an optional fixed-length attribute.in the attributes table of the ClassFile (?4.2) structure. A class must have an EnclosingMethod attribute if and only if it is a local class or an anonymous class. A class may have no more than one EnclosingMethod attribute.
 
The EnclosingMethod attribute has the following format:
 
EnclosingMethod_attribute {
    u2 attribute_name_index;
    u4 attribute_length;
    u2 class_index
    u2 method_index;
}
 
The items of the EnclosingMethod_attribute structure are as follows:
 
attribute_name_index
 
The value of the attribute_name_index item must be a valid index into the constant_pool table. The constant_pool entry at that index must be a CONSTANT_Utf8_info (?4.5.7) structure representing the string "EnclosingMethod".
 
attribute_length
 
The value of the attribute_length item is four.
 
class_index
 
The value of the class_index item must be a valid index into the constant_pool table. The constant_pool entry at that index must be a CONSTANT_Class_info (?4.5.1) structure representing a the innermost class that encloses the declaration of the current class.
 
method_index
 
If the current class is not immediately enclosed by a method or constructor, then the value of the method_index item must be zero. Otherwise, the value of the method_index item must be a valid index into the constant_pool table. The constant_pool entry at that index must be a CONSTANT_NameAndType_info (?4.5.6) structure representing a the name and type of a method in the class referenced by the class_index attribute above. It is the responsibility of the Java compiler to ensure that the method identified via the method_index is indeed the closest lexically enclosing method of the class that contains this EnclosingMethod attribute.