fixed issue 18

[oleksandr-pavlyk]

Fixes #18.

Using vanilla numpy:

In [1]: import numpy as np
   ...: x = np.zeros([2, 3])
   ...: y = np.fft.fftpack.rfftn(x, axes=[1], norm='ortho')
   ...:
   ...:

In [2]: import mkl_fft, mkl_fft._numpy_fft

In [3]: y2 = mkl_fft._numpy_fft.rfftn(x, axes=[1], norm='ortho')

In [4]: np.allclose(y, y2)
Out[4]: True

In [5]: import numpy as np
   ...: x = np.ones([2, 3])
   ...: y = np.fft.fftpack.rfftn(x, axes=[1], norm='ortho')
   ...:
   ...:

In [6]: y2 = mkl_fft._numpy_fft.rfftn(x, axes=[1], norm='ortho')

In [7]: np.allclose(y, y2)
Out[7]: True