Expose the default handlers

This allows an implementation to reuse one of the implementations
if they would like to implement a replacement for the other.

conn.go

@@ -160,7 +160,7 @@ func Dial(address string) (*Conn, error) {
 	if err != nil {
 		return nil, err
 	}
-	return newConn(tr, newDefaultHandler(), newDefaultSignalHandler())
+	return newConn(tr, NewDefaultHandler(), NewDefaultSignalHandler())
 }
 
 // DialHandler establishes a new private connection to the message bus specified by address, using the supplied handlers.
@@ -174,7 +174,7 @@ func DialHandler(address string, handler Handler, signalHandler SignalHandler) (
 
 // NewConn creates a new private *Conn from an already established connection.
 func NewConn(conn io.ReadWriteCloser) (*Conn, error) {
-	return NewConnHandler(conn, newDefaultHandler(), newDefaultSignalHandler())
+	return NewConnHandler(conn, NewDefaultHandler(), NewDefaultSignalHandler())
 }
 
 // NewConnHandler creates a new private *Conn from an already established connection, using the supplied handlers.

default_handler.go

@@ -18,7 +18,10 @@ func newIntrospectIntf(h *defaultHandler) *exportedIntf {
 	return newExportedIntf(methods, true)
 }
 
-func newDefaultHandler() *defaultHandler {
+//NewDefaultHandler returns an instance of the default
+//call handler. This is useful if you want to implement only
+//one of the two handlers but not both.
+func NewDefaultHandler() *defaultHandler {
 	h := &defaultHandler{
 		objects:     make(map[ObjectPath]*exportedObj),
 		defaultIntf: make(map[string]*exportedIntf),
@@ -214,7 +217,10 @@ func (obj *exportedIntf) isFallbackInterface() bool {
 	return obj.includeSubtree
 }
 
-func newDefaultSignalHandler() *defaultSignalHandler {
+//NewDefaultSignalHandler returns an instance of the default
+//signal handler. This is useful if you want to implement only
+//one of the two handlers but not both.
+func NewDefaultSignalHandler() *defaultSignalHandler {
 	return &defaultSignalHandler{}
 }