ftp/tnftp: Adopt/Update to 20230409

ChangeLog:

* Release as "tnftp 20230409".
* Use better terminology.
* Merge NetBSD ftp from 20210826 to 20230226:
	- Add option sslnoverify to control validation of SSL
	  certificates.
	- Add netrc processing to fetch-mode (URL on command line) to
	  enable options and autologin via netrc.
	- Fix SSL cleanup in some error paths.
	- Support SSL certificate validation by default.
	  FTPSSLNOVERIFY=1 in the environment to disable validation.
	- Handle relative URLs.
	- Improve ftp(1) markup.
	- Fix -? in a more portable manner.
	- Equivalent to "NetBSD-ftp 20230225" with documentation and
	  portability fixes.