Convert a relative path to an absolute one.
CL_String CL_VirtualDirectory::make_path_absolute( const CL_String & relative_path);
Detailed description:
If CL_VirtualFileSystem was not set, this function uses CL_PathHelp::path_type_file If CL_VirtualFileSystem is set, this function uses CL_PathHelp::path_type_virtual param: relative_path = The relative path