Support: Properly check for IE9 absolute scrollbox mishandling

[gibson042]

Summary

Account for some IE9 quirks that were even stranger than first glance suggested, and add support assertions to fix broken tests.

Fixes gh-3699 (for real)
Fixes gh-3730

   raw     gz Sizes
271034  80335 dist/jquery.js
 87145  30139 dist/jquery.min.js

   raw     gz Compared to master @ 3fcddd6e72e7e318c0b062e391d60867732318ae
   +87    +16 dist/jquery.js
   +34     +2 dist/jquery.min.js

Checklist

• All authors have signed the CLA at https://cla.js.foundation/jquery/jquery
• New tests have been added to show the fix or feature works
• Grunt build and unit tests pass locally with these changes
• If needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com