Add and update include guards

Include guards in most changed files were missing, I added them keeping
the same style as other SDL files. In some cases I moved the include
guards around to be the first thing the header has to take advantage of
any possible improvements compiler may have for inclusion guards.

src/render/software/SDL_blendline.h

@@ -18,10 +18,16 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+
+#ifndef SDL_blendline_h_
+#define SDL_blendline_h_
+
 #include "../../SDL_internal.h"
 
 
 extern int SDL_BlendLine(SDL_Surface * dst, int x1, int y1, int x2, int y2, SDL_BlendMode blendMode, Uint8 r, Uint8 g, Uint8 b, Uint8 a);
 extern int SDL_BlendLines(SDL_Surface * dst, const SDL_Point * points, int count, SDL_BlendMode blendMode, Uint8 r, Uint8 g, Uint8 b, Uint8 a);
 
+#endif /* SDL_blendline_h_ */
+
 /* vi: set ts=4 sw=4 expandtab: */