textual: standardize some "cannot read" and "seek failed" error messages

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
libfdisk: (dos) correct the grammar of the disk-identifier prompt

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
libfdisk: (dos) improve the grammar of an error message

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
libfdisk: (gpt) use consistent final period in status messages

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
losetup: cut the remaining little block of help text into slices too

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
cytune: fix glush typo in cytune

Signed-off-by: Rafael Ferreira <rafael.f.f1@gmail.com>