dtach: Update to 0.9

pkgsrc changes:
- Add LICENSE

Changes:
0.9
---
- Added AIX support.
- Added dtach -N, a mode similar to dtach -n, except dtach will stay in the
  foreground instead of daemonizing.
- Added dtach -p, which copies the contents of standard input to a session.
- dtach will no longer send 255 bytes of garbage to the program when read()
  returns an error.
- The executable bit is now set on the socket if clients are attached, and
  cleared when all clients have detached.
- The initial state of signals such as SIGPIPE are now preserved when
  executing the program, instead of having the program start with some signals
  ignored.
- A buffer overflow no longer occurs when a long socket path name is used, and
  dtach will now try to use chdir to get around the length limitation if
  necessary.

(leot)