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
bitnot(PG_FUNCTION_ARGS)
{
	VarBit	   *arg = PG_GETARG_VARBIT_P(0);
	VarBit	   *result;
	bits8	   *p,
			   *r;
	bits8		mask;

	result = (VarBit *) palloc(VARSIZE(arg));
	SET_VARSIZE(result, VARSIZE(arg));
	VARBITLEN(result) = VARBITLEN(arg);

	p = VARBITS(arg);
	r = VARBITS(result);
	for (; p < VARBITEND(arg); p++)
		*r++ = ~*p;

	/* Pad the result */
	mask = BITMASK << VARBITPAD(result);
	if (mask)
	{
		r--;
		*r &= mask;
	}

	PG_RETURN_VARBIT_P(result);
}

bitnot(PG_FUNCTION_ARGS)
{
	VarBit	   *arg = PG_GETARG_VARBIT_P(0);
	VarBit	   *result;
	bits8	   *p,
			   *r;
	bits8		mask;

	result = (VarBit *) palloc(VARSIZE(arg));
	SET_VARSIZE(result, VARSIZE(arg));
	VARBITLEN(result) = VARBITLEN(arg);

	p = VARBITS(arg);
	r = VARBITS(result);
	for (; p < VARBITEND(arg); p++)
		*r++ = ~*p;

	/* Pad the result */
	mask = BITMASK << VARBITPAD(result);
	if (mask)
	{
		r--;
		*r &= mask;
	}

	PG_RETURN_VARBIT_P(result);
}
