On a Contribution page without a PriceSet, the selector changes in !8 (merged) seemed to break that use-case.
Also calls the "pricefieldvisibility" init function, because since dom elements were created, the two extensions kind of step on each other's feet. It's a hack of a solution, but mostly harmless (requires an update of the pricefieldvisiblity ext).
cc @brienne could you check at a glance if this seems OK to you? We weren't sure where the selector is from, and there are so many combos of CiviCRM contribution forms to support, so we figured may as well support both classes.
