current tty as returned from ttyname(3) so it can try to avoid writing to
the current tty if possible. Previously, it did this by trimming off any
leading directory (effectively performing a basename(3) on the path
returned from ttyname(3)). However, this chopped off too much of the path
for ttys who have directories in their name such as pts(4). Instead, just
strip off the leading /dev/ from the path returned by ttyname(3). This
fixes write(1) when using pts(4).
MFC after: 1 week
Reported by: rwatson
a4cc298ac9