Ongoing crusade fixes

Not much to show for a lot of effort, but I'm aware of numerous other uncovered cases and unintentional side-effects of the current crusade CB now (and the events) and poised to fix those in the future.  Nothing is game-breaking or requiring critical attention.  Also, I've now confirmed at least one flaw in vanilla's CB too, FWIW.

BTW, though I did confirm that you can easily move CB support code out of the critical path in the CB and into events while retaining all necessary information (FROM => FROMFROM & ROOT => FROM, as logical), the final fix for the nested-PREVs issue was to simply not nest them and rely on the fact that the CB is **check_de_jure_tier = KING**, simply using *kingdom* in place of *PREV*.

/slap

I did confirm that the old code, in either case, was not working at all due to scope problems-- even when the holder was already in the right hands and under simplified conditions for the *any_de_jure_vassal_title* limit (the new, fancy *liege_before_war* condition remains untested-- replaced with a dummy to focus on the scope problems).

This is not a conclusion: crusades are a few fixes away from done.  Even the final bugfix is flawed (but at least does something correct most of the time, unlike before).  I ran out of time.

As for my quest to discover the hidden magic of how nested PREV scoping works in CKII, the gist of **that** conclusion: there is no hidden magic.  Apparently, CKII doesn't even have the EU4 behavior to which I alluded.  It always just breaks and does almost never what you want it to do.  When it does, it's a coincidence.  Never nest PREV, unless you truly want to pop multiple levels of the stack at once (and never be able to reference where you were within the new scope).