Design 3 development checkpoint

Design 3 development checkpoint

Sigh. The testing is forcing me to realize several misconceptions I've
been carrying.

Status:

This code is design 3. There are three refactors that clearly need to be
addressed immediately:

1. Design 3 is vulnerable to notification stack URL hacking, which has
   to be fixed by shifting to designs 3.1 or (unlikely) 4.
2. Fall back to rsync only on RRDP download failure; it's wasteful to
   also do it on RRDP validation failure.
3. Must commit repository content at the RPP level, not at the module
   level. (One failing RPP should not invalidate the whole module.)