Add proper and reliable (i hope) support for modifier keys

backends/x/unicode.go

@@ -1,6 +1,6 @@
 package x
 
-import "fmt"
+// import "fmt"
 import "unicode"
 import "github.com/jezek/xgb/xproto"
 import "github.com/jezek/xgbutil/keybind"
@@ -138,7 +138,7 @@ func (backend *Backend) keycodeToButton (
 	var selectedKeysym xproto.Keysym
 	var selectedRune   rune
 
-	fmt.Printf("AAA\t%X\t%X\t%X\t%X\n", symbol1, symbol2, symbol3, symbol4)
+	// fmt.Printf("AAA\t%X\t%X\t%X\t%X\n", symbol1, symbol2, symbol3, symbol4)
 	
 	// big ol list in the middle
 	switch {