Don’t adjust CRLF in file names

Don’t adjust CRLF in file names

* doc/misc/gnus.texi (Non-ASCII Group Names):
* etc/NEWS:
* test/lisp/net/tramp-tests.el (tramp--test-utf8):
Use utf-8-unix, not utf-8, for default-file-name-coding-system, so
that CRLF in file names is left alone.
* lisp/international/mule-cmds.el (set-default-coding-systems):
Do not alter CRLF in file name coding systems.
(prefer-coding-system): Ignore differences in CRLF processing when
checking whether we used the user-specified file name coding system.
* test/src/fileio-tests.el: New file.