Deprecate splinter_set_av() for splinter_set_scrub()

[splinterhq]

Originally, I called Splinter's hygiene mode "auto vacuum" because I wanted to use a relatable term. But, it's not really all that applicable to something with static geometry - and doesn't need to be run for even close to the same reasons as relational database vacuum does.

I'm just going to call it what it is, "scrub", and implement a single API for it:

int splinter_set_as_mode(mode);
enum splinter_get_as_mode(const char *store);

Or something very similar.