Fixes several issues:
- It was not possible to correctly trace where instances were coming from in a
REPL. This led to them being pretty much ignored.
- Instances were then just treated as classes and not as actual instances in
MixedObjects. (However since they were ignored in the first place this
wasn't really an issue).
- Avoiding the repr bug https://github.com/python/cpython/pull/2132/files in
Jedi is working a bit differently. We're just never accessing Objects
directly. This should work around 99.99% of the cases were people are using
this stuff.
Fixes#872