box2d: when copying actually copy exactly rather than using init to enforce validity - closes #749

src/box2d.cpp

@@ -51,9 +51,15 @@ box2d<T>::box2d(const coord<T,2> &c0,const coord<T,2> &c1)
 
 template <typename T>
 box2d<T>::box2d(const box2d &rhs)
-{
+    : minx_(rhs.minx_),
+      miny_(rhs.miny_),
+      maxx_(rhs.maxx_),
+      maxy_(rhs.maxy_) {}
+// copy rather than init so dfl ctor (0,0,-1,-1) is not modified
+// http://trac.mapnik.org/ticket/749
+/*{
     init(rhs.minx_,rhs.miny_,rhs.maxx_,rhs.maxy_);
-}
+}*/
 
 template <typename T>
 #if !defined(__SUNPRO_CC)