epm-sh-functions: don't use tput -S directly

bin/epm-sh-functions

@@ -59,36 +59,35 @@ check_tty()
 	is_command tput || return
 	# FreeBSD does not support tput -S
 	echo | a= tput -S >/dev/null 2>/dev/null || return
-	[ -z "$USETTY" ] || return
-	export USETTY=1
+	USETTY="tput -S"
 }
 
 : ${BLACK:=0} ${RED:=1} ${GREEN:=2} ${YELLOW:=3} ${BLUE:=4} ${MAGENTA:=5} ${CYAN:=6} ${WHITE:=7}
 
 set_boldcolor()
 {
-	[ "$USETTY" = "1" ] || return
+	[ -n "$USETTY" ] || return
 	{
 		echo bold
 		echo setaf $1
-	} |tput -S
+	} | $USETTY
 }
 
 set_color()
 {
-	[ "$USETTY" = "1" ] || return
+	[ -n "$USETTY" ] || return
 	{
 		echo setaf $1
-	} |tput -S
+	} | $USETTY
 }
 
 restore_color()
 {
-	[ "$USETTY" = "1" ] || return
+	[ -n "$USETTY" ] || return
 	{
 		echo op; # set Original color Pair.
 		echo sgr0; # turn off all special graphics mode (bold in our case).
-	} |tput -S
+	} | $USETTY
 }
 
 echover()