add generics to methods currently returning raw types

There are several methods that return raw java.util.Enumeration. Adding a type parameter would return the potential for misuse, produce cleaner and safer code and give a better development experience since you don't need to look up the the JavaDoc, the IDE automatically inserts the right type.

The affected methods are:

* javax.jms.QueueBrowser.getEnumeration() should return Enumeration
* javax.jms.Message#getPropertyNames() should return Enumeration
* javax.jms.JMSProducer#getPropertyNames() should return Enumeration
* javax.jms.MapMessage#getMapNames() should return Enumeration
* javax.jms.ConnectionMetaData#getJMSXPropertyNames() should return Enumeration
#### Affected Versions
[2.0PD]

Start by locating the five listed JMS API method declarations: QueueBrowser.getEnumeration(), Message#getPropertyNames(), JMSProducer#getPropertyNames(), MapMessage#getMapNames(), and ConnectionMetaData#getJMSXPropertyNames(). Review the surrounding API definitions and build or compatibility checks. Done means all five declarations expose the specified Enumeration element types consistently.

Written by the indexing model from the issue text.