Sort definitions of SMV models to reduce recursion depth in typecheck

[mgudemann]

This fixes #17 (superseeding #26 as EBMC code has changed)

[kroening]

How about using a std::stack?

[mgudemann]

For the topological sort? Sure, but this is implemented in cbmc/src/util/graph.h so it would require a change to CBMC.

[kroening]

For the topological sort? Sure, but this is implemented in cbmc/src/util/graph.h so it would require a change to CBMC.

No, to replace the recursion. Then you don't need the topological sort anymore.

[mgudemann]

I thought about changing this to using a stack, but this requires more work in typecheck_expr_rec and the functionality is already implemented using topsort. If this PR is not included, maybe the topsort should also be removed from CBMC because at the time I added it for this specific reason. It probably only affects SMV files converted from AIG.

[kroening]

#1040