Predict integer overflow to avoid buffer overruns.

Several functions, mostly type input functions, calculated an allocation
size such that the calculation wrapped to a small positive value when
arguments implied a sufficiently-large requirement.  Writes past the end
of the inadvertent small allocation followed shortly thereafter.
Coverity identified the path_in() vulnerability; code inspection led to
the rest.  In passing, add check_stack_depth() to prevent stack overflow
in related functions.

Back-patch to 8.4 (all supported versions).  The non-comment hstore
changes touch code that did not exist in 8.4, so that part stops at 9.0.

Noah Misch and Heikki Linnakangas, reviewed by Tom Lane.

Security: CVE-2014-0064
make_bound_box(POLYGON *poly)
{
	int			i;
	double		x1,
				y1,
				x2,
				y2;

	if (poly->npts > 0)
	{
		x2 = x1 = poly->p[0].x;
		y2 = y1 = poly->p[0].y;
		for (i = 1; i < poly->npts; i++)
		{
			if (poly->p[i].x < x1)
				x1 = poly->p[i].x;
			if (poly->p[i].x > x2)
				x2 = poly->p[i].x;
			if (poly->p[i].y < y1)
				y1 = poly->p[i].y;
			if (poly->p[i].y > y2)
				y2 = poly->p[i].y;
		}

		box_fill(&(poly->boundbox), x1, x2, y1, y2);
	}
	else
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("cannot create bounding box for empty polygon")));
}

make_bound_box(POLYGON *poly)
{
	int			i;
	double		x1,
				y1,
				x2,
				y2;

	if (poly->npts > 0)
	{
		x2 = x1 = poly->p[0].x;
		y2 = y1 = poly->p[0].y;
		for (i = 1; i < poly->npts; i++)
		{
			if (poly->p[i].x < x1)
				x1 = poly->p[i].x;
			if (poly->p[i].x > x2)
				x2 = poly->p[i].x;
			if (poly->p[i].y < y1)
				y1 = poly->p[i].y;
			if (poly->p[i].y > y2)
				y2 = poly->p[i].y;
		}

		box_fill(&(poly->boundbox), x1, x2, y1, y2);
	}
	else
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("cannot create bounding box for empty polygon")));
}
