Fix import array in extensions.

- import arrays in extensions (mako file).
- put import_arrays in converter,
  along the lines of our own objects (numpy and triqs uses
  the same capsule technique, i.e. the standard technique from python
  doc.)

pytriqs/wrap_generator/wrapper.mako.cpp

@@ -1001,6 +1001,9 @@ ${f.code};
 PyMODINIT_FUNC
 init${module.name}(void)
 {
+    // import numpy
+    import_array();
+
     PyObject* m;
 
 %for c in module.classes.values() :

triqs/arrays/python/array_view_to_python.hpp

@@ -31,7 +31,7 @@ namespace triqs { namespace arrays { namespace numpy_interface  {
 
  template<typename ArrayViewType >
   PyObject * array_view_to_python ( ArrayViewType const & A, bool copy=false) {
-   _import_array();
+   //_import_array();
    typedef typename ArrayViewType::value_type value_type;
    static const int rank = ArrayViewType::rank;
    const int elementsType (numpy_to_C_type<typename boost::remove_const<value_type>::type>::arraytype);

triqs/arrays/storages/mem_block.hpp

@@ -130,7 +130,7 @@ namespace triqs { namespace arrays { namespace storages { //namespace details {
   static_assert(!std::is_const<ValueType>::value, "internal error");
 
 #ifdef TRIQS_WITH_PYTHON_SUPPORT
-  static void import_numpy_array() { if (_import_array()!=0) TRIQS_RUNTIME_ERROR <<"Internal Error in importing numpy";}
+  static void import_numpy_array() {}// if (_import_array()!=0) TRIQS_RUNTIME_ERROR <<"Internal Error in importing numpy";}
 #endif
 
   //Construct to state 0

triqs/python_tools/wrapper_tools.hpp

@@ -368,12 +368,25 @@ template <typename T, int N> struct py_converter<triqs::utility::mini_vector<T,N
 
 // --- array
 
+inline void import_numpy() {
+  static bool init = false;
+  if (!init) {
+    _import_array();
+    std::cerr << "importing array"<<std::endl;
+    init = true;
+  }
+}
+
 template <typename ArrayType> struct py_converter_array {
- static PyObject *c2py(ArrayType const &x) { return x.to_python(); }
+ static PyObject *c2py(ArrayType const &x) {
+  import_numpy();
+  return x.to_python();
+ }
  static ArrayType py2c(PyObject *ob) {
   return ArrayType (ob);
  }
  static bool is_convertible(PyObject *ob, bool raise_exception) {
+  import_numpy();
   try {
    py2c(ob);
    return true;