Import tmux

We have to use SOCK_SEQPACKET instead of SOCK_STREAM for client/server
communication, because UDS does things with control messages that tmux
does not expect.

Change-Id: I3edb1875d61fb976cf6485c650f4fd4b82fa354c

etc/mtree/NetBSD.dist.base

@@ -117,6 +117,8 @@
 ./usr/share/doc/psd/19.curses
 ./usr/share/doc/usd
 ./usr/share/doc/usd/03.shell
+./usr/share/examples
+./usr/share/examples/tmux
 ./usr/share/info
 ./usr/share/games
 ./usr/share/games/fortune

etc/mtree/NetBSD.dist.tests

@@ -162,7 +162,6 @@
 ./usr/share/doc/kyua-atf-compat
 ./usr/share/doc/kyua-cli
 ./usr/share/doc/kyua-testers
-./usr/share/examples
 ./usr/share/examples/atf
 ./usr/share/examples/kyua-cli
 ./usr/share/examples/lutok