improved traceback error messages

[John W. Eaton]

On  6-Aug-2008, Søren Hauberg wrote:

| tir, 05 08 2008 kl. 22:13 -0400, skrev John W. Eaton:
| > With the changes I checked in, it will print:
| > 
| >   error: operator +: nonconformant arguments (op1 is 2x2, op2 is 4x4)
| >   error: called from:
| >   error:   /scratch/jwe/build/octave/h.m at line 8, column 9
| >   error:   /scratch/jwe/build/octave/g.m at line 6, column 9
| >   error:   /scratch/jwe/build/octave/f.m at line 4, column 5
| 
| this is great! Thanks for doing this. Attached is a changeset that
| changes the error texts in the manual to match the new style.

I added some ChangeLog entries and checked in these changes.

Thanks,

jwe