copy, pop, get, getitem, setdefault
Also add read steps to taint tracking.
Reading from a tainted collection can be done in two situations:
1. There is an acces path
In this case a read step (possibly from a flow summary)
gives rise to a taint step.
2. There is no access path
In this case an explicit taint step (possibly via a flow
summary) should exist.
Apparently the fixup of .expected in the latest commit was only required
when extracting as Python 3, but not as Python 2... I honestly don't
understand why.
