The changes to meas_algorithms and pipe_tasks were trivial. The change to ip_diffim was significantly larger and resulted in changes to numerous files. This has resulted in Policy being removed from the package completely apart from in the deprecation wrapper.

Kian-Tat Lim please can you take a look. There are a couple of outstanding questions:

1. Should I move the policy deprecation to utils or somewhere since I could use it in meas_algorithms.
2. You mentioned copying out the parts we need from the PropertySet rather than copying the entire PropertySet but do we want that subtle change in behavior where every value will be required even if before it was allowed to be missing depending on other values?

I do still need to add the deprecation statement in pex_config makePolicy.

We decided not to put a pex_policy dependency into utils, and that copying out PropertySet items into a custom config class would be excessive.

Minor comments in ip_diffim.  Looks good.