Problem:  The glob() function on Unix-like systems does not escape
          newline characters when expanding wildcards. A maliciously
          crafted string containing '\n' can be used as a command
          separator to execute arbitrary shell commands via
          mch_expand_wildcards(). This depends on the user's 'shell'
          setting.
Solution: Add the newline character ('\n') to the SHELL_SPECIAL
          definition to ensure it is properly escaped before being
          passed to the shell (pyllyukko).