Make gdk_keyval_to_unicode return more codes

Previously, we didn't map ASCII controls to their Unicode
counterparts. Fix that.

https://bugzilla.gnome.org/show_bug.cgi?id=644836

gdk/gdkkeyuni.c

@@ -831,6 +831,16 @@ static const struct {
 
   /* Following items added to GTK, not in the xterm table */
 
+  /* A few ASCII control characters */
+
+  { 0xFF08 /* Backspace */, '\b' },
+  { 0xFF09 /* Tab       */, '\t'  },
+  { 0xFF0A /* Linefeed  */, '\n' },
+  { 0xFF0B /* Vert. Tab */, '\v' },
+  { 0xFF0D /* Return    */, '\r' },
+  { 0xFF1B /* Escape    */, '\033' },
+  { 0xFFFF /* Delete    */, '\177' },
+
   /* Numeric keypad */
 
   { 0xFF80 /* Space     */, ' ' },