check_server_features: setting to retrieve the features of a ftp-server

To get an overview of the implemented features of an ftp-server an "FEAT" command is always issued.

With the parameter "check_server_features=false" sending this command to the server can be suppressed.

Default is "false".

Example for the server-response of a FEAT:

[info] ..ftp server reply [FEAT]: 211-Features:
EPRT
EPSV
MDTM
PASV
REST STREAM
SIZE
TVFS
211 End