CTextBox: ensure paint of text and background only if required

It's not new, but this involves also other properties,
like color or position...

It's possible that more properties are required, maybe needs to be watched
and evaluation of comparison might require further revisions.

src/gui/widget/textbox.h

@@ -116,9 +116,12 @@ class CTextBox
 		int  getFontTextHeight();
 
 		/* Variables */
-		std::string m_cText;
+		std::string m_cText, m_old_cText;
 		std::vector<std::string> m_cLineArray;
 
+		int m_old_x, m_old_y, m_old_dx, m_old_dy, m_old_nBgRadius, m_old_nBgRadiusType, m_old_nMode;
+		fb_pixel_t m_old_textBackgroundColor;
+
 		bool m_showTextFrame;
 
 		CBox m_cFrame;