[manual] suggested addition to pcolor description

[John W. Eaton]

On  4-Feb-2009, Ben Abbott wrote:

| Using "interpolate 0,0" the result renders very rapidly.
| 
| Petr, Thanks for pointing out my err, the result looks very good to  
| me. The corrected changeset is attached ... attributed to you of  
| course ;-)

I applied it.

| I don't have a copy of an old gnuplot available. Petr are your running  
| Octave built from the developer's sources? If so, can you verify that  
| this change does not break anything?

It works fine for me with 4.2.2.

jwe