libtizcore: avoid reading non-shared object entries during directory scanning

[juanrubio]

Files other than .so files should not be tried while scanning the plugin locations

e.g.:

 while ((p_dir_entry = readdir (p_dir)))
            {
              if (p_dir_entry->d_name[0] != '.'
                  && p_dir_entry->d_name[strlen (p_dir_entry->d_name) - 1]
                       != 'a')