Moved Registry::ReadFileCallback + WriteFileCallback, and osgDB::ReaderWriter::Options into their own separate Options file and into the osgDB namespace.

Introduced a new callback osgDB::FindFileCallback that overrides the default behavior of findDataFile/findLibraryFile.

Introduced support for assigning ReaderWriter::Options directory to PagedLOD.

Introduced new osgDB::FileLocationCallback for assistancing the DatabasePager to know when a file is hosted on a local or remote file system.

include/osgDB/FileCache

@@ -28,6 +28,8 @@ class OSGDB_EXPORT FileCache : public osg::Referenced
 
         const std::string& getFileCachePath() const { return _fileCachePath; }
 
+        virtual bool isFileAppropriateForFileCache(const std::string& originalFileName) const;
+
         virtual std::string createCacheFileName(const std::string& originalFileName) const;
 
         virtual bool existsInCache(const std::string& originalFileName) const;