Add a convenience constructor to pass a String instead of a list of InetSocketAddress

I am using Spring 3 and want to pass the list of servers through a property.
Having to do the following is not convenient:
```
                <constructor-arg>
                        <list>
                                <bean class="java.net.InetSocketAddress">
                                        <constructor-arg>
                                                <value>localhost</value>
                                        </constructor-arg>
                                        <constructor-arg>
                                                <value>12000</value>
                                        </constructor-arg>
                                </bean>
                                <bean class="java.net.InetSocketAddress">
                                        <constructor-arg>
                                                <value>localhost</value>
                                        </constructor-arg>
                                        <constructor-arg>
                                                <value>12001</value>
                                        </constructor-arg>
                                </bean>
                        </list>
                </constructor-arg>
```

So this change just add a convenience constructor to pass a String. This string being parsed by AddrUtil.getAddresses()

Now I can just pass the following:
```<constructor-arg value="${my.memcache.servers}"/>```