Minimize for octagons

[sim642]

The original octagon library implements and documents a minimization algorithm. The Apron implementation of octagon minimization is missing:

apron/octagons/oct_representation.c

Lines 269 to 275 in 3cc1f26

	/* NOT IMPLEMENTED: do nothing */
	void oct_minimize(ap_manager_t* man, oct_t* a)
	{
	oct_internal_t* pr = oct_init_from_manager(man,AP_FUNID_MINIMIZE,0);
	ap_manager_raise_exception(man,AP_EXC_NOT_IMPLEMENTED,pr->funid,
	"not implemented");
	}

Although the original implementation has a separate space-efficient storage format for minimized octagons, Apron clearly does not. Nevertheless, the algorithm could still be implemented to just act on and return the half-matrix representation (or really just modify it in-place).

It wouldn't offer actual space savings, but it would be useful for printing and to_lincons_array to have the octagon minimzed, such that they don't return an incomprehensibly large set of redundant constraints.