tests_mercury doesn't return the same thing on mac and linux

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On linux, the test goes correctly and say that the original and f90 versions 
return the same thing. 

But on mac, there is difference for the MVS algorithm and I don't know why. I 
should check that when I have time. This is probably a compilator issue but it 
is intriguing nonetheless.

Original issue reported on code.google.com by [email protected] on 31 Jan 2013 at 8:12