[manual] suggested addition to pcolor description

[Francesco Potorti`]

In Two-Dimensional Plots I read:

 -- Function File:  pcolor (X, Y, C)
 -- Function File:  pcolor (C)
     Density plot for given matrices X, and Y from `meshgrid' and a
     matrix C corresponding to the X and Y coordinates of the mesh.  If
     X and Y are vectors, then a typical vertex is (X(j), Y(i),
     C(i,j)).  Thus, columns of C correspond to different X values and
     rows of C correspond to different Y values.

     *See also:* meshgrid, contour.

To the end of the description I would add four sentences that explain
how pcolor interprets its arguments and how it differs from imagesc.

Of the four sentences below, the first and last are the most important,
while the second and third are optional:

1)
Notice that values from C are taken as the values of the vertices of
the mesh, meaning that the resulting plot contains rows(C)-1 rows and
columns(C)-1 columns.

2)
The colors used for plotting are computed by interpolating the values at
the four vertices of each rectangle of the grid.

3)
Currently, gnuplot does no interpolation, but displays a color
corresponding to the lower left vertex of the rectangle.

4)
If you want your plot to show one color (rectangle?) for each of the
values in C, you can use imagesc (see).