Preliminary pg upsert support

[zealot128]

Implemented two ways,

1. "naive upsert" for pg < 9.5

insert into, on exception update all the things.

2. real upsert since 9.5

INSERT INTO .... ON CONFLICT id DO UPDATE SET ...

Also included a fix for exporting ActsAsTaggableOn - AATO adds it's own "tag_list" as a virtual attribute into the record.attributes, thus, is included in the "INSERT" statement.

The ac88b32 fixes that problem by comparing the attributes with column_names.

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Would be nice if some user PG user would test it...

[jakeonfire]

@zealot128 if you wouldn't mind rebasing master and getting a green build, we can finally merge this 😅

[zealot128]

@zealot128 if you wouldn't mind rebasing master and getting a green build, we can finally merge this 😅

Squashed rebase is pushed. Let me know if there are any other issues.

[jakeonfire]

looks like there is one legitimate exception:

expect { adapter.on_duplicate_key_update(double(), double()) }.to raise_error('on_duplicate: :override is not currently supported in the PostgreSQL adapter')

makes sense. can you fix the spec? otherwise i may be able to help at some point.