The ability to ventcrawl is now checked by the /handle_ventcrawl() proc, making it possible to properly check before and after the do_after() call.
Moves various checks into the base can_ventcrawl proc.
Now lists the first object that prevents a mob from ventcrawling, making it easier to correct the exception list.
Removes the issmall() check, instead checks if the crawling mob has the relevant verb. Fixes#14081.
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