Added include guard to math_for_graphics.h

polygon/math_for_graphics.h

+#ifndef MATH_FOR_GRAPHICS_H
+#define MATH_FOR_GRAPHICS_H
 // math stuff for graphics, from FreePCB
 
 /* Function FindLineSegmentIntersection
@@ -61,3 +63,5 @@ double GetPointToLineSegmentDistance( int x, int y, int xi, int yi, int xf, int
 double GetPointToLineDistance( double a, double b, int x, int y, double * xp=NULL, double * yp=NULL );
 
 double Distance( double x1, double y1, double x2, double y2 );
+
+#endif