Fix.

Former-commit-id: d8c9912a87cae9b37bd512a8fe576d856f6b9903

include/igl/covariance_scatter_matrix.cpp

@@ -13,6 +13,7 @@
 #include "edges.h"
 #include "verbose.h"
 #include "cat.h"
+#include "PI.h"
 
 IGL_INLINE void igl::covariance_scatter_matrix(
   const Eigen::MatrixXd & V, 

include/igl/cross_field_missmatch.cpp

@@ -17,6 +17,7 @@
 #include <igl/vertex_triangle_adjacency.h>
 #include <igl/triangle_triangle_adjacency.h>
 #include <igl/rotation_matrix_from_directions.h>
+#include <igl/PI.h>
 
 namespace igl {
   template <typename DerivedV, typename DerivedF, typename DerivedM>