[Osi] OsiCpx writeLp not working

[Lou Hafer]

Matt,

	I can't comment on the rationale behind the design of OsiCpx; I'm not
sufficiently familiar with Cplex to make recommendations.  But the overall
principle is that the various OsiXXX interfaces should be interchangeable.
Quirks of the underlying solver should be hidden.  Cplex can do what it likes in
terms of rewriting the system, but this should remain invisible to a client
using Cplex through OsiCpx.  By extension, OsiCpx should not expose quirks of
Cplex, or of the interface layer, to the client.  In particular, the client
should not know about choice of caching strategy.  OsiCpx should use whatever
intelligence it can muster to make a good decision, but the client should not
get a direct vote.

       Exposing the options of the underlying solver is the expedient solution.
The challenge is to achieve the same result in a generic way --- to either build
the necessary intelligence into the OsiXXX interface so that it can diagnose the
situation and instruct the underlying solver, or come up with a hint that tells
any OsiXXX `here's the situation; adapt yourself as best you can'.

							Lou