Isolate perennial behaviors and entry points that operate on SHAs

[samreid]

The main distinguishing characteristic of perennial is that it can operate on SHAs of perennial-alias. It seems important to demarcate the subset of perennial functionality that is about SHA operations. Perhaps a dedicated directory in perennial. We should make an effort to minimize tasks that forward from chipper to perennial, limiting it to the ones that perform SHA operations. It has been very confusing lately to be working in perennial and perennial-alias and not knowing which in getting invoked when, and after pushing a change having to pull the opposite repo right away to keep in sync.

[zepumph]

Investigation of this will start over in #401