[pmc] rpa: fixed clone with offsets

This is now the last known rpa bug, all tests pass.
Need to check still if we can skip some WBs now.
[pmc] finalize rewrite, add clone tests, fix WBs

add WBs for all writes and changes.
add ChangeLog for all the changes in the smoke-me/rpa-offset-gh1152 branch.
Closes #1152, #1153, #1154.

Performance win with parrot-bench:
22.8% on linux 64bit, the fastest parrot since 2.8.0
15.5% on darwin