wall: send message also to sessions opened by user 'sleeper'

Ignoring an user by name, and not telling about it in manual page, is
unexpected.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
last: fix typo

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
wall: sync usage() with howto-usage-function.txt

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
mesg: sync usage() with howto-usage-function.txt

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
wall: line wrap at column 79 also when line has tab chars

Earlier tabs caused random ragged right indentation, because the tab
length was assumed to be 1 char which is not the case most of the time.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
docs: add --present to last(1) manual page

I forgot to update manual after writing this functionality.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
docs: add note to wall.1 about sessions which will not get message

Sessions that has in utmp data ut_line begining with ':' are skipped.
This is done to avoid write errors to devices such as '/dev/:0'.  For
example wdm is reported to to generate such utmp line.

Perhaps in future this choise should be revalidated.  If utmp data
contains rubbish it might be best to raise write errors about such rather
than trying to fix the issue by skipping suspicious device entries.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
write: make test if writing to terminal is possible simple

Earlier test failed when user had write permission, but was not in
special group that owns terminal devices, usually tty.

This made write(1) to fail for root, if the root did not happen to be in
tty group.  In this commit root is granted ot write to anyone, even if
they have mesg(1) turned off.  For an user who is trying to write to own
other session the group write bit is significant only for whether mesg(1)
are enabled.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>