add test for keyword arguments passed into cdef functions with optional arguments, fix parameter names in test

--HG--
rename : tests/run/simplify_calls.pyx => tests/run/cdef_function_kwargs.pyx

convert function argument names in libc declarations to lower case to make their use as keyword arguments more natural

improve error reporting on mapped keyword arguments for C functions, implement out-of-order keywords and C method mapping

Fix runtime crash as described on cython-devel.

__pyx_CyFunctionObject.defaults must be fully zeroed or a segfault or
memory corruption may occur if the object is visited by the garbage
collector before defaults is later populated. Uninitialized memory is
cast to PyObject* with undefined results:

  static int __Pyx_CyFunction_traverse(__pyx_CyFunctionObject *m, visitproc visit, void *arg)
  {
      ...
      if (m->defaults) {
          PyObject **pydefaults = __Pyx_CyFunction_Defaults(PyObject *, m);
          int i;
          for (i = 0; i < m->defaults_pyobjects; i++)
              Py_VISIT(pydefaults[i]);
                       ^^^^^^^^^^^^^

refactor analyse_types() and friends to work more like a transform by returning the node or a replacement

simple optimisation that statically maps keyword arguments to positional arguments when called signature is known