textual: fix a few typos in some of the usage help texts

Also improve clarity of some other lines of those texts.

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
textual: remove inconsistent periods from two error messages

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
textual: tag two bug messages as "internal error"

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
textual: gettextize several overlooked messages

Also improve the clarity of some of them.

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
textual: standardize reporting of program name plus package version

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
renice: correct the usage synopsis, and improve help text

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
renice: accept also -V for --version, and document it

Also improve the man page.

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
textual: use UTIL_LINUX_VERSION everywhere

Signed-off-by: Karel Zak <kzak@redhat.com>