AP_Math: compiler warning: is_zero special case for vector3.h in a template

libraries/AP_Math/vector3.h

@@ -51,8 +51,10 @@
 #define VECTOR3_H
 
 #include <math.h>
+#include <float.h>
 #include <string.h>
 
+
 #if defined(MATH_CHECK_INDEXES) && (MATH_CHECK_INDEXES == 1)
 #include <assert.h>
 #endif
@@ -154,7 +156,8 @@ public:
     bool is_inf(void) const;
 
     // check if all elements are zero
-    bool is_zero(void) const { return x==0 && y == 0 && z == 0; }
+    bool is_zero(void) const { return (fabsf(x) < FLT_EPSILON) && (fabsf(y) < FLT_EPSILON) && (fabsf(z) < FLT_EPSILON); }
+
 
     // rotate by a standard rotation
     void rotate(enum Rotation rotation);