TST: don't use numpy.stack for numpy 1.9 compatiblity
TST: don't use numpy.stack for numpy 1.9 compatiblity

PyWavelets/pywt,eriol/pywt,michelp/pywt,rgommers/pywt,PyWavelets/pywt,rgommers/pywt,michelp/pywt,eriol/pywt,rgommers/pywt,rgommers/pywt,eriol/pywt,grlee77/pywt,michelp/pywt,grlee77/pywt