mdtm too early for server

[Alexander V. Lukyanov]

---> MDTM 20121028072217 lftptest.bat
<--- 550 20121028072217 lftptest.bat: No such file or directory*

This error just means that the server does not support overloaded MDTM
command. Probably there is no way to change modification time of a file
on this server.

lftp supports onlt 4 ways to set the time: MFMT, SITE UTIME (2 variants)
and overloaded MDTM.