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
circle_out(PG_FUNCTION_ARGS)
{
	CIRCLE	   *circle = PG_GETARG_CIRCLE_P(0);
	char	   *result;
	char	   *cp;

	result = palloc(2 * P_MAXLEN + 6);

	cp = result;
	*cp++ = LDELIM_C;
	*cp++ = LDELIM;
	if (!pair_encode(circle->center.x, circle->center.y, cp))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not format \"circle\" value")));

	cp += strlen(cp);
	*cp++ = RDELIM;
	*cp++ = DELIM;
	if (!single_encode(circle->radius, cp))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not format \"circle\" value")));

	cp += strlen(cp);
	*cp++ = RDELIM_C;
	*cp = '\0';

	PG_RETURN_CSTRING(result);
}

circle_out(PG_FUNCTION_ARGS)
{
	CIRCLE	   *circle = PG_GETARG_CIRCLE_P(0);
	char	   *result;
	char	   *cp;

	result = palloc(2 * P_MAXLEN + 6);

	cp = result;
	*cp++ = LDELIM_C;
	*cp++ = LDELIM;
	if (!pair_encode(circle->center.x, circle->center.y, cp))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not format \"circle\" value")));

	cp += strlen(cp);
	*cp++ = RDELIM;
	*cp++ = DELIM;
	if (!single_encode(circle->radius, cp))
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not format \"circle\" value")));

	cp += strlen(cp);
	*cp++ = RDELIM_C;
	*cp = '\0';

	PG_RETURN_CSTRING(result);
}
