Fix argument to array() in array._bind_param()

array.__init__() expects a list as its sole parameter but inside _bind_param(), instead of sending a list it's sending each item in the list as a separate argument which is incorrect.
- flake8 all of test/dialect/postgresql
- add __backend__ to most tests so that pg8000 can start coming in
Merge remote-tracking branch 'origin/pr/124' into issue3141
- Fixed bug in :class:`.postgresql.array` object where comparison
to a plain Python list would fail to use the correct array constructor.
Pull request courtesy Andrew.  fixes #3141