_lp_connection: correctly detect local connection if X11 display doesn't start with colon

Created by: mpasternacki

FreeBSD with slim display manager sets DISPLAY=unix:0.0, which is currently detected as telnet session and displayed in ugly red.

[japhy:~] % who am i
japhy            pts/3        28 Aug 16:36 (unix:0.0)
[japhy:~] % echo $DISPLAY
unix:0.0
[japhy:~] % uname -a
FreeBSD sophon.local 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r333486: Fri May 11 12:32:05 UTC 2018     maciej@hatter:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG  amd64

It's quite likely that this renders the previous condition (x"$whoami" = *'(:'*) redundant, but I didn't want to remove it without confirmation.