Work was done for 6.0 beta 3 to delay rendering of pages until renders

all completed, in order to avoid page jumps. That work regressed some

unit tests, which were no longer testing the correct state.
This fixes those tests by better mirroring the body element and

relevant containers all within $testsScratch, resetting their styling,

and managing states while testing to ensure we're working with the

equivalent of the styles used while loading a page. It then tests the

newer visibility states expected during and after page load.

JavaScript unit tests all pass on Firefox and Chrome.