sysutils/screen: Option to disable socketdir

Some users may prefer not to have screen sockets in /tmp/screens (EUID== 0)
and /tmp/uscreens (EUID != 0), preferring instead to keep screen sockets in
the user's home directory. Enabling the NOSOCKETDIR option accomplishes
this.

Reported by: "John W. O'Brien" <john@saltant.com>
MFH: 2022Q2