Improved getters on entities to support the relational model transparently.

- Entity manager now infers indexing based on a heuristic (when they're used
  for relational accesses.)
- Superposition now proxies calls to __get__.

BUG=
R=scudette@gmail.com

Review URL: https://codereview.appspot.com/97940043
Pslist and psxview now list dead procs (from the allocator).

DarwinProcessFilter moved to pslist module because of dependencies.

BUG=
R=scudette@gmail.com

Review URL: https://codereview.appspot.com/94010046