ALL: Remove trailing whitespaces

This tries to make our code a bit more compliant with our code formatting
conventions. For future use, this is the command I used:
  git ls-files "*.cpp" "*.h" | xargs sed -i -e 's/[ \t]*$//'

backends/platform/sdl/sdl.h

@@ -30,7 +30,7 @@
 #include "backends/events/sdl/sdl-events.h"
 #include "backends/log/log.h"
 
-/** 
+/**
  * Base OSystem class for all SDL ports.
  */
 class OSystem_SDL : public ModularBackend {
@@ -38,7 +38,7 @@ public:
 	OSystem_SDL();
 	virtual ~OSystem_SDL();
 
-	/** 
+	/**
 	 * Pre-initialize backend. It should be called after
 	 * instantiating the backend. Early needed managers are
 	 * created here.