The previous approach of emitting a severe log message when a
state (descriptor) was unknown was misleading. There are valid cases
where some states are not known, if, for example, a module was
explicitly disabled.
Using Builder.failOnUnknownStates() in unit tests is far cleaner, as
the existence of unknown states is tested in a controlled environment:
one where are states are supposed to be known.
ExtensionElement is now a marker interface that requires all
implementation non-abstract classes to carry a static final QNAME
field (of type QName). This is verified by a new unit test.
Also FullyQualifiedElement is renamed to simply XmlElement. XmlElement
is used over ExtensionElement when implementing classes do not
statically know the qualified name of the XML elements they
represent. In general, XmlElement should be used sparingly, and every
XML element should be modeled by its own Java class (implementing
ExtensionElement).
This is a complete redesign of what was previously
XmppNioTcpConnection. The new architecture allows to extend an XMPP
client to server (c2s) connection with new transport bindings and
other extensions.
