Added love.keyboard.setTextInput to enable/disable text input events (enabled by default.)

This fixes the issue of receiving an unwanted text input event if a key is used to bring a game's textbox into focus, since textinput events can be triggered after keypress events if the keypress generates text.

src/modules/keyboard/sdl/Keyboard.h

@@ -51,6 +51,9 @@ public:
 	bool hasKeyRepeat() const;
 	bool isDown(Key *keylist) const;
 
+	void setTextInput(bool enable);
+	bool hasTextInput() const;
+
 private:
 
 	bool key_repeat;