Merge pull request #376 from kintel/skip_longfilenames

Also skip .files and _files with long filenames. I think its better than before. If somebody dislikes it, or wants additional configuration, it can be done in a future step. Thanks, Marius, and nice to have you helping!

Marlin/cardreader.cpp

     {
       if (p.name[0] == DIR_NAME_FREE) break;
       if (p.name[0] == DIR_NAME_DELETED || p.name[0] == '.'|| p.name[0] == '_') continue;
+      if (longFilename[0] != '\0' &&
+          (longFilename[0] == '.' || longFilename[0] == '_')) continue;
       if ( p.name[0] == '.')
       {
         if ( p.name[1] != '.')