screen: fix launch.

When screen isn't suid, it can't create the directory under /run/screens
for sessions to sit in. We went with the approach of creating the
directory at boot time instead of removing --with-socket-dir so screen
would default to using ~/.screen, because it would require users with
currently running screen sessions to launch the screen client with
SCREENDIR set correctly, and an INSTALL.msg to warn users.

srcpkgs/screen/files/20-screen.sh

@@ -0,0 +1 @@
+install -dm 1777 /run/screens

srcpkgs/screen/template

@@ -1,7 +1,7 @@
 # Template file for 'screen'
 pkgname=screen
 version=4.8.0
-revision=3
+revision=4
 build_style=gnu-configure
 configure_args="--with-sys-screenrc=/etc/screenrc --enable-pam
  --enable-colors256 --enable-rxvt_osc --enable-telnet
@@ -25,4 +25,6 @@ post_install() {
 	if [ "$build_option_multiuser" ]; then
 		chmod 4755 ${DESTDIR}/usr/bin/screen-${version}
 	fi
+
+	vinstall $FILESDIR/20-screen.sh 644 etc/runit/core-services
 }