LOCK: other commands used during transfer NOOP, ABOR

[antbryan]

1. At least three commands are documented to work while a transfer is in
   progress. STAT, which reports the status of the transfer, NOOP, which does
   nothing (but many clients use to keep the control connection open when a
   firewall might close it over a long data transfer), and ABOR, which stops an
   existing transfer. My suggestion would be that STAT will return a response
   after the data transfer has finished (after the response from the transfer
   completion); NOOP the same; ABOR will interrupt the transfer, the transfer's
   end response will be signaled as interrupted, and the ABOR command will send
   a 426 and 226.

[antbryan]

STAT is now documented with Tim's suggestion:

The STAT command and Telnet IP and Synch signals are not allowed during a running transfer.