mkdir, split: write --verbose output to stdout, not stderr.

mkdir, split: write --verbose output to stdout, not stderr.

* src/mkdir.c (verbose_output): New function.
(announce_mkdir): Use it.
* src/split.c (usage): Update.
* src/split.c (cwrite): Write to stdout, not stderr.
* doc/coreutils.texi (split invocation): Remove the mention
of --verbose output being printed to stderr.
* tests/mkdir/p-v: Redirect stdout, not stderr.
* tests/misc/split-a: Likewise.
* NEWS: Mention this change.
* TODO: Remove this item.