Add SGR 9 strikethrough to test file.

test/display.txt

@@ -4,11 +4,11 @@ Test of all features involved in do_text()
 Reverse video + red on yellow:       bing! 
 Yellow on red should look the same:  bong! 
 
-Basic attrs, combining chars, both widths: Bold blink underline [Λ̊][チ][text]
-Wide char should be off by 1 narrow char: Bold blink underline [Λ̊][チ][text]
+Basic attrs, combining chars, both widths: Bold blink under strike [Λ̊][チ][text]
+Wide char should be off by 1 narrow char: Bold blink under strike [Λ̊][チ][text]
 
 Double width, double height. Should be red top, magenta bottom, blue DW only:
-#3Bold blink underline [Λ̊][チ][text]
-#4Bold blink underline [Λ̊][チ][text]
-#6Bold blink underline [Λ̊][チ][text]
+#3Bold blink under strike [Λ̊][チ][text]
+#4Bold blink under strike [Λ̊][チ][text]
+#6Bold blink under strike [Λ̊][チ][text]