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
point_div(PG_FUNCTION_ARGS)
{
	Point	   *p1 = PG_GETARG_POINT_P(0);
	Point	   *p2 = PG_GETARG_POINT_P(1);
	Point	   *result;
	double		div;

	result = (Point *) palloc(sizeof(Point));

	div = (p2->x * p2->x) + (p2->y * p2->y);

	if (div == 0.0)
		ereport(ERROR,
				(errcode(ERRCODE_DIVISION_BY_ZERO),
				 errmsg("division by zero")));

	result->x = ((p1->x * p2->x) + (p1->y * p2->y)) / div;
	result->y = ((p2->x * p1->y) - (p2->y * p1->x)) / div;

	PG_RETURN_POINT_P(result);
}

point_div(PG_FUNCTION_ARGS)
{
	Point	   *p1 = PG_GETARG_POINT_P(0);
	Point	   *p2 = PG_GETARG_POINT_P(1);
	Point	   *result;
	double		div;

	result = (Point *) palloc(sizeof(Point));

	div = (p2->x * p2->x) + (p2->y * p2->y);

	if (div == 0.0)
		ereport(ERROR,
				(errcode(ERRCODE_DIVISION_BY_ZERO),
				 errmsg("division by zero")));

	result->x = ((p1->x * p2->x) + (p1->y * p2->y)) / div;
	result->y = ((p2->x * p1->y) - (p2->y * p1->x)) / div;

	PG_RETURN_POINT_P(result);
}
