scaling for polyfit.m [patch]

[Thomas Weber]

Hi, 

some time ago we had a bug[1] filed in Debian against polyfit.m; it
breaks down for large values of x (which is known and a problem in
Matlab as well). 

Based on the idea of the bug reporter, I've changed the polyfit function
to always apply scaling, making it work for large x values.

The patch is attached; it includes a test with the data provided in the
bugreport. 

One thing where I was unsure is which polynomial to use for calculating
the values of S; I've taken the scaled polynomial because I think most
people want the conditition value for the actual calculation.

[1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=348480

Regards
        Thomas

polyfit.diff
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