BLD: Move python-including header to start of special/_gufuncs.cpp

Found in the process of trying to build on Cygwin in #6

scipy/special/_gufuncs.cpp

@@ -1,7 +1,7 @@
+#include "ufunc.h"
 #include "special/bessel.h"
 #include "special/legendre.h"
 #include "special/sph_harm.h"
-#include "ufunc.h"
 
 using namespace std;