Polyfit with scaling

[Dmitri A. Sergatskov]

Looks good, though i have a couple minor comments:

-- if std(x) == 0 then it means that all x are the same number (I
would also argue that one
    may want to compare to eps rather than 0). In that case we cannot
do any fits,
    so probaly should just exit with an error.

-- I really do not like have variables that different only in
capitalization: x and X in this code.
    I would rename X to XX or something. But this is matter of taste
and I would leave it to
    jwe to have the final say.

Thanks!

Dmitri.
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