add time, gap, and absgap arguments to solver.minimize/maximize

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These will allow the user to specify a maximum amount of time to run before
stopping, or a gap value the solver can use to stop.

We should also expose gap and absgap attributes on the solution, if
possible.  That way we'll know how far the best solution is from optimality.

{{{
    # In this case the solver will stop when any of the following are true:
    #   - the solver has run for at least 300 seconds
    #   - gap <= 5%
    #   - abs(dual - primal) <= 10
    solver.minimize(time=300, gap=0.05, absgap=10)
}}}

Original issue reported on code.google.com by ryan%che...@gtempaccount.com on 7 Jul 2009 at 6:38

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Original comment by ryan%che...@gtempaccount.com on 20 Jul 2009 at 3:37

• Changed state: Fixed