Prepend ${_chroot} to a pathname in a consistent and robust way:

insert a slash between ${_chroot} and the pathname if and only if
${_chroot} is set to a non-empty string.  Now the pathname is very
likely to be absolute, but we shouldn't take that for granted.

etc/rc.subr

@@ -261,7 +261,8 @@ _find_processes()
 
 	_pref=
 	if [ $_interpreter != "." ]; then	# an interpreted script
-		read _interp < ${_chroot:-}/$_procname	# read interpreter name
+						# read interpreter name
+		read _interp < ${_chroot}${_chroot:+"/"}$_procname
 		_interp=${_interp#\#!}		# strip #!
 		set -- $_interp
 		case $1 in
@@ -613,7 +614,7 @@ run_rc_command()
 				return 1
 			fi
 
-			if [ ! -x ${_chroot}${command} ]; then
+			if [ ! -x ${_chroot}${_chroot:+"/"}${command} ]; then
 				warn "run_rc_command: cannot run $command"
 				return 1
 			fi