further issues with iteration

[<pl...@pi...>]

Hi,

a further manifestation of the way iteration substitutions can be unhelpful.

  plot for [date in "1894 1802"] "dataset-".date."+.hFFT.dat"
 
           ^
    Bad data on line 2


in case that does not display consistently on various formats please 
note that the caret is aligned under the double-quote following .date. 
end before the plus sign.

It is clearly unhelpful that we don't know which manifestation  of [date 
in "1894 1802"]  causes the problem.

Since messing with display of the caret and the command line may lead to 
further confusion and may even be counter productive, perhaps it would 
be useful for the error message to append information of the value of 
the iteration value when iteration is present.

eg.

    Bad data on line 2 , during iteration : date = "1894"

best regards, Peter.