* doc/wget.texi: updated documentation to reflect the new FTPS functionality.
* src/ftp-basic.c (ftp_greeting): new function to read the server's greeting.
(ftp_login): greeting code was previously here. Moved to ftp_greeting to
support FTPS implicit mode.
(ftp_auth): wrapper around the AUTH TLS command.
(ftp_ccc): wrapper around the CCC command.
(ftp_pbsz): wrapper around the PBSZ command.
(ftp_prot): wraooer around the PROT command.
* src/ftp.c (get_ftp_greeting): new static function.
(init_control_ssl_connection): new static function to start SSL/TLS on the
control channel.
(getftp): added hooks to support FTPS commands (RFCs 2228 and 4217).
(ftp_loop_internal): test for new FTPS error codes.
* src/ftp.h: new enum 'prot_level' with available FTPS protection levels +
prototypes of previous functions. New flag for enum 'wget_ftp_fstatus' to track
whether the data channel has some security mechanism enabled or not.
* src/gnutls.c (struct wgnutls_transport_context): new field 'session_data'.
(wgnutls_close): free GnuTLS session data before exiting.
(ssl_connect_wget): save/resume SSL/TLS session.
* src/http.c (establish_connection): refactor ssl_connect_wget call.
(metalink_from_http): take into account SCHEME_FTPS as well.
* src/init.c, src/main.c, src/options.h: new command line/wgetrc options.
(main): in recursive downloads, check for SCHEME_FTPS as well.
* src/openssl.c (struct openssl_transport_context): new field 'sess'.
(ssl_connect_wget): save/resume SSL/TLS session.
* src/retr.c (retrieve_url): check new scheme SCHEME_FTPS.
* src/ssl.h (ssl_connect_wget): refactor. New parameter of type 'int *'.
* src/url.c. src/url.h: new scheme SCHEME_FTPS.
* src/wget.h: new FTPS error codes.
* src/metalink.h: support FTPS scheme.
