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/sensor/SDL_sensor_c.h

@@ -18,6 +18,10 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+
+#ifndef SDL_sensor_c_h_
+#define SDL_sensor_c_h_
+
 #include "SDL_config.h"
 
 struct _SDL_SensorDriver;
@@ -35,4 +39,6 @@ extern void SDL_SensorQuit(void);
 /* Internal event queueing functions */
 extern int SDL_PrivateSensorUpdate(SDL_Sensor *sensor, float *data, int num_values);
 
+#endif /* SDL_sensor_c_h_ */
+
 /* vi: set ts=4 sw=4 expandtab: */