Returning a generic would allow for
List<ExtensionElement> list = stanza.getExtension("foo", "bar");
to compile (Note the we are calling getExtension(), not
getExtension*s*()).
Users are encouraged to use the type safe getExtension(Class<? extends
ExtensionElement) variant instead.
Fixes SMACK-825.
Adopt to common design patterns in Smack:
- getFrom(Packet) in Packetextensions
- INSTANCES.put() in getInstanceFor()
- ELEMENT instead of ELEMENT_NAME
- Use XmlStringBuilder
Florian Schmaus