install_all_fixtures() does not install fixtures declared with the inherit_from attribute

[julozi]

The install_all_fixtures() method ignores fixtures declared with the inherit_from attribute.
I'm using version 0.4.5

[julozi]

I notice this bug appears only when loading multiple fixtures file in a single load() call.
If I load each file each fixtures file in a separate load() call, install_all_fixtures() works fine.

[mtustin-handy]

In fact, what happens is that the individual file names become top level keys, as opposed to the expected behaviour of loading each file at a time, where the keys are the top-level objects within the files.

[mtustin-handy]

In fact, it's fairly clear that this is the root of the problem: https://github.com/uber/charlatan/blame/6c8fd8b4f20f465bc473b5e99b652c33c5002898/charlatan/fixtures_manager.py#L124-L126

[tuler]

Loading each file individually does work but then we can't use cross-file references the way it should be (i.e. !rel otherfile.user), as the fixture keys are not prefixed by the filename.