library: find tty device name of process quicker

library: find tty device name of process quicker

The procps library attempts to work out the tty of a process
through several methods. For things like /dev/tty123 or
/dev/foo it works fine.

For tty devices that put the minor number in a directory
of the major name this fails. So then we have to fallback
to stating things like the processes STDERR and try again.

Considering a lot of processes sit on ttys such as
/dev/pts/3 this is a lot of wasted time. At the point of
entering driver_name we know "/dev/pts" and we know "3"
we just didn't join them up the right way as this is old
code.

This change now looks for /dev/pts/3 as well. It does it
after looking for /dev/pts3 so the behaviour is the same.

References:
 https://bugs.debian.org/770215

Signed-off-by: Craig Small <csmall@enc.com.au>