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.
Introduced a new FindFileCallback to Registry to compliement the existing ReadFileCallback and WriteFileCallback.
Added support for assign Find, Read and WriteFileCallbacks to osdDB::Options to enable plugins/applications to override the callbacks just for that
read/write call and any nested file operations