Codechange: Use override specifer for overriding member declarations

This is a C++11 feature that allows the compiler to check that a virtual
member declaration overrides a base-class member with the same signature.

Also src/blitter/32bpp_anim_sse4.hpp +38 is no longer erroneously marked
as virtual despite being a template.

src/script/api/script_text.hpp

@@ -45,7 +45,7 @@ public:
 	RawText(const char *text);
 	~RawText();
 
-	/* virtual */ const char *GetEncodedText() { return this->text; }
+	const char *GetEncodedText() override { return this->text; }
 private:
 	const char *text;
 };