Partially revert "Work-around preprocessor issues on Windows."

Commit 99be617278 moved the #undef from
SceneGraph/Camera3D.h to Math/Matrix4.h, but it seems that it needs to
be in both places.

src/Math/Matrix4.h

@@ -22,7 +22,7 @@
 #include "Matrix.h"
 #include "Point3D.h"
 
-#ifdef WIN32 /* I so HATE windows.h */
+#ifdef _WIN32 /* I so HATE windows.h */
 #undef near
 #undef far
 #endif

src/SceneGraph/Camera3D.h

@@ -21,6 +21,11 @@
 
 #include "AbstractCamera.h"
 
+#ifdef _WIN32 /* I so HATE windows.h */
+#undef near
+#undef far
+#endif
+
 namespace Magnum { namespace SceneGraph {
 
 /**