[FIX] document_ftp: allow to use '..' command when traveling in ftp directories

lp bug: https://launchpad.net/bugs/734892 fixed

bzr revid: mat@openerp.com-20140121103021-mv9gcv4iprary0ac

addons/document_ftp/ftpserver/abstracted_fs.py

@@ -260,6 +260,7 @@ class abstracted_fs(object):
         if path == '/' and mode in ('list', 'cwd'):
             return (None, None, None )
 
+        if path == '..': path = self.cwd + '/..'
         path = _to_unicode(os.path.normpath(path)) # again, for '/db/../ss'
         if path == '.': path = ''