Added thread safe ref/unref by default.

include/osgText/Font

@@ -199,6 +199,9 @@ public:
     {
     public:
     
+        FontImplementation():
+            osg::Referenced(true) {}
+    
         virtual std::string getFileName() const = 0;
 
         /** Set the pixel width and height hint.*/

src/osgText/Font.cpp

@@ -139,6 +139,7 @@ osgText::Font* osgText::readFontStream(std::istream& stream, const osgDB::Reader
 
 
 Font::Font(FontImplementation* implementation):
+    osg::Object(true),
     _width(16),
     _height(16),
     _margin(1),