Merged in zpl's changes for FTP and Telnet 0.65k)

Merged in zpl's changes. The FTP server is not yet reliable, in
particular trying to delete a file via FTP after copying another may
result in the Duet rebooting due to the webserver module getting stuck
in a spin loop. Also the copied file has on one occasion been observed
to be shorter than the original.
Fixed FTP bug and added binary (version 0.65k-dc42)

Fixed buffer overrun bug in FTP LIST command that caused a subsequent
FTP delete command to crash. Increased file list buffer to 2000 bytes.
Added binary RepRapFirmware-057k-dc42.bin.