[Osi] Add setCoeff method to set the coefficient of a column within a given row?

[Christophe-Marie Duquesne]

I would absolutely love to see this included in Osi.

An explanation for Osi not offering this method in the default
interface can probably be found in glpk: I recently had to play with
the glpk interface, and the only methods I know about for setting
coefficients in the problem matrix are:
glp_set_mat_row - set (replace) row of the constraint matrix
glp_set_mat_col - set (replace) column of the constraint matrix
glp_load_matrix- load (replace) the whole constraint matrix

That being say, I can probably come up with a patch that will do the
trick (not very efficiently), using glp_get_mat_row and
glp_get_mat_col to retrieve a row/column and insert the value at the
right place.

Any other solver where this could be tricky?