[Coin-lpsolver] OsiSimplexInterface behaviour

[Lou Hafer]

 << Context is behaviour of solvers when OsiSimplexInterface is enabled.
    Question (broadly) is the effect/implications of asking a solver to
    perform a pivot sequence that might normally be considered a violation
    of the rules for the current simplex phase. >>

	Does a solver really need to be `in a phase' at all times? Well, no,
not really. The various checks (in dylp, at least) really are sanity checks.
Given a phase, you can assume certain things shouldn't happen. That allows
some simplifications in the code. Violations are normally a good indication
of a coding error. So being in a phase serves a useful purpose.

	Now I've written that last paragraph, I guess I'd say the real problem
is that dylp assumes that if it's doing simplex pivots, then it's in one of
primal I, primal II, or dual II. It probably wouldn't be too difficult to add
a `no phase' phase (:-) to various specific routines (pivot, factorization).

	What sort of behaviour would be expected at the transition back to
solver control? Would the solver be allowed to assess it's state and proceed
accordingly?

							Lou