storage of the path lists into osgDB::Registry, and changed the data
structor from a char* to a std::deque. Changed a names of couple of the
convinience functions in osgDB/FileUtils to better reflect the two
public FilePathList's - DataFilePathList and the LibraryFilePathList.
Added support into the osgDB::Registry::readNode/Image/Object methods
for pushing and popping the path of the current file being loaded.
