Throw UnsupportedOperationException for unsupported ForkChannel.connect() methods

[cfredri4]

ForkChannel.connect(String cluster_name, boolean useFlushIfPresent) and ForkChannel.connect(String cluster_name, Address target, long timeout, boolean useFlushIfPresent) are not overridden in ForkChannel and will call subclass JChannel. This change instead makes them throw UnsupportedOperationException. This change also corrects the javadoc that a closed ForkChannel can be reused (it cannot).