Improved normest

[Marco Caliari]

Dear maintainers,

I have seen changeset 
http://hg.savannah.gnu.org/hgweb/octave/rev/87595d714005 about normest, by 
Jaroslav. As already discussed, the choice

x = norm (A, "columns").'

for the initial vector leads to wrong values (second largest eigenvalue) 
for some "important" matrices, like

toeplitz([-2,1,zeros(1,2)]), toeplitz([-2,1,zeros(1,4)]), etc

This was the reason for the old random initial vector. I agree it is not 
nice to have slightly different results at each run, but it is not nice to 
have wrong values, too.

Best regards,

Marco