Escape double-quotes in MKD/CDUP/CWD/PWD responses
Escape double-quotes in MKD/CDUP/CWD/PWD responses

Per RFC959, double-quotes in response paths should be doubled-up.

fix asylumfunk#36

oleksiyk/nodeftpd,impaler/nodeftpd,sstur/nodeftpd,phillipgreenii/nodeftpd