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
QTNSort(QTNode *in)
{
	int			i;

	/* since this function recurses, it could be driven to stack overflow. */
	check_stack_depth();

	if (in->valnode->type != QI_OPR)
		return;

	for (i = 0; i < in->nchild; i++)
		QTNSort(in->child[i]);
	if (in->nchild > 1)
		qsort((void *) in->child, in->nchild, sizeof(QTNode *), cmpQTN);
}

QTNSort(QTNode *in)
{
	int			i;

	/* since this function recurses, it could be driven to stack overflow. */
	check_stack_depth();

	if (in->valnode->type != QI_OPR)
		return;

	for (i = 0; i < in->nchild; i++)
		QTNSort(in->child[i]);
	if (in->nchild > 1)
		qsort((void *) in->child, in->nchild, sizeof(QTNode *), cmpQTN);
}
