Add some recursion and looping defenses in prepjointree.c.

Add some recursion and looping defenses in prepjointree.c.

Andrey Lepikhov demonstrated a case where we spend an unreasonable
amount of time in pull_up_subqueries().  Not only is that recursing
with no explicit check for stack overrun, but the code seems not
interruptable by control-C.  Let's stick a CHECK_FOR_INTERRUPTS
there, along with sprinkling some stack depth checks.

An actual fix for the excessive time consumption seems a bit
risky to back-patch; but this isn't, so let's do so.

Discussion: https://postgr.es/m/703c09a2-08f3-d2ec-b33d-dbecd62428b8@postgrespro.ru