[Couenne] SetCutoff()

[Francois Margot]

Hi:

In Couenne/stable/0.3, the code for CouenneProblem::setCutoff(double
value) always sets the value to 

cutoff + SafeCutoff * (1. + fabs(cutoff))

where SafeCutoff is 1e-4. While that might be safe, it might also be
disastrous for problems with many optimal solutions or many feasible
solutions within SafeCutoff * (1. + fabs(optimal_value)) of the optimal
value. While it might be a reasonable thing to do in some situations, it
seems that when the code claims to have found a feasible solution with
value v, the cutoff should be set to v, not slightly higher.

I also noted that Couenne/stable/0.3 (downloaded today) does not
terminate on nvs19. On a Fedora 13 (linux 64 bits) install, I get:

Cbc0015I Node 175 Obj -1103.72 Unsat 100 depth 88
## WEAK  up-br: [ 9.00000000 ,(9.00000000)] -> 9.00000000

and then the last line repeats with no end. This is using 

bb_log_level 3
variable_selection osi-strong

and all other defaults as in the provided couenne.opt file.

Francois