cbrt test failure on Win32/MSVC

[Michael Goffioul]

Hi,

While analyzing test failures under Win32/MSVC I found that cbtr(0) ->
NaN. while the expected value is 0. MSVC does not provide cbrt
implementation, so the octave implementation is used, but that
implementation definitely returns NaN when the argument is 0 (because
it computes 0/0). Shouldn't the test be changed, as it's weird to have
a test that is known to fail when using octave's own code?

Michael.