Summary
-------

Add methods addAll, which adds a set of elements in a collection to the JList and JComboBox.

Problem
-------

There is currently no straight forward way of adding a Collection to a DefaultListModel and DefaultComboBoxModel. Shown below is the typical way clients add multiple elements to the model:

DefaultListModel<Integer> lm = new DefaultListModel<>();
List<Integer> lst = IntStream.range(0, 50).collect(ArrayList::new, ArrayList::add, ArrayList::addAll);

for (int i =0; i < lst.size(); i++) {
          lm.add(i);
}

The above method requires more code from the client side, and also results in unnecessary events being generated for each insertion.

Solution
-------

Solution is to add new api addAll, that takes a collection of items and add them all at once.  Here is the webrev containing the proposed changes: http://cr.openjdk.java.net/~kaddepalli/4842658/webrev05/

Specification
-------

Providing the public methods that are being affected here: 

1. src/java.desktop/share/classes/javax/swing/DefaultComboBoxModel.java

```
    /**
     * Adds all of the elements present in the collection.
     * 
     * @param c the collection which contains the elements to add
     * @throws NullPointerException if {@code c} is null
     */
    public void addAll(Collection<? extends E> c)

    /**
     * Adds all of the elements present in the collection, starting
     * from the specified index.
     * 
     * @param index index at which to insert the first element from the
     * specified collection
     * @param c the collection which contains the elements to add
     * @throws ArrayIndexOutOfBoundsException if {@code index} does not 
     * fall within the range of number of elements currently held
     * @throws NullPointerException if {@code c} is null
     */
    public void addAll(int index, Collection<? extends E> c)
```
   2. src/java.desktop/share/classes/javax/swing/DefaultListModel.java

```
    /**
     * Adds all of the elements present in the collection to the list.
     *
     * @param c the collection which contains the elements to add
     * @throws NullPointerException if {@code c} is null
     */
    public void addAll(Collection<? extends E> c)

    /**
     * Adds all of the elements present in the collection, starting
     * from the specified index.
     * 
     * @param index index at which to insert the first element from the 
     * specified collection
     * @param c the collection which contains the elements to add
     * @throws ArrayIndexOutOfBoundsException if {@code index} does not
     * fall within the range of number of elements currently held
     * @throws NullPointerException if {@code c} is null
     */
    public void addAll(int index, Collection<? extends E> c)
```