Method numpy.ndarray.tostring() is deprecated in favor of tobytes() in 1.9

[AndrewUshakov]

This deprecated (see at accepted pull request numpy/numpy#15867) method is used 6 times in the file netCDF4/_netCDF4.pyx and may be somewhere else so each call to this method causes output of "DeprecationWarning: tostring() is deprecated. Use tobytes() instead." to stderrr.

[jameshiebert]

I'd like to +1 this issue. We have a repositories of modest length that use netCDF4 and their test suites now come up with tens of thousands of warning messages!

DeprecationWarning: tostring() is deprecated. Use tobytes() instead.

Should be a pretty simple fix.

[AndrewUshakov]

Thank you!