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
poly_overabove(PG_FUNCTION_ARGS)
{
	POLYGON    *polya = PG_GETARG_POLYGON_P(0);
	POLYGON    *polyb = PG_GETARG_POLYGON_P(1);
	bool		result;

	result = polya->boundbox.low.y >= polyb->boundbox.low.y;

	/*
	 * Avoid leaking memory for toasted inputs ... needed for rtree indexes
	 */
	PG_FREE_IF_COPY(polya, 0);
	PG_FREE_IF_COPY(polyb, 1);

	PG_RETURN_BOOL(result);
}

poly_overabove(PG_FUNCTION_ARGS)
{
	POLYGON    *polya = PG_GETARG_POLYGON_P(0);
	POLYGON    *polyb = PG_GETARG_POLYGON_P(1);
	bool		result;

	result = polya->boundbox.low.y >= polyb->boundbox.low.y;

	/*
	 * Avoid leaking memory for toasted inputs ... needed for rtree indexes
	 */
	PG_FREE_IF_COPY(polya, 0);
	PG_FREE_IF_COPY(polyb, 1);

	PG_RETURN_BOOL(result);
}
