SFTP: support '*' prefix for quote operations

prefixing a command with '*' means it is allowed to fail without
aborting the chain actions

lib/ssh.h

@@ -115,6 +115,7 @@ struct ssh_conn {
   char *quote_path1;          /* two generic pointers for the QUOTE stuff */
   char *quote_path2;
   LIBSSH2_SFTP_ATTRIBUTES quote_attrs; /* used by the SFTP_QUOTE state */
+  bool acceptfail;            /* accept file in SFTP_QUOTE state */
   char *homedir;              /* when doing SFTP we figure out home dir in the
                                  connect phase */