confusing close / cleanup functions.

[danlipsa]

from @durack1

I personally find it confusing that we have vcs.clean_auto_generated_objects(), vcs.clear(), vcs.close(), vcs.destroy(), vcs.flush(), vcs.onclosing(), vcs.removeP() and vcs.removeobject(), it's really not intuitive to me what each of these functions do, and how they overlap. It may be obvious to someone else, but it certainly isn't to me without considerable guidance.