Update parrot to version 4.0.0.

Upstream changes:

- Core
  + Several cleanups to the interp subsystem API
  + Cleanups and documentation additions for green threads and timers
  + Iterator PMC and family now implement the "iterator" role
  + A bug in Parrot_ext_try was fixed where it was not popping a
    context correctly
- Documentation
  + Docs for all versions of Parrot ever released are now available
    at http://parrot.github.com
- Tests
  + Timer PMC tests were converted from PASM to PIR

(he)