Identify and test py3-beautifulsoup4 / py3-soupsieve cycle

[smoser]

soupsieve declares in pypi that they have 'null' requirements_dist. An attempt to use soupsieve without beautifulsoup4 will result in import error.

beautifulsoup4 in pypi identifies they need soupsieve. An attempt to import beautifulsoup4 (bs4) without soupsieve will runtime-warn.