Fix duplicate detection to work with JSON arrays

[villasv]

So the issue isn't as simple as I hoped initially, sorry for the previous broken build. Here's the conundrum previously happening:

• If you don't serialize, the syntax will fail when the JSON field contains arrays because the SQLite dialect doesn't handle arrays properly (SQLite doesn't have array types).
• If you do serialize the entire object, the comparison fails on PostgreSQL where you can't compare JSON and string, and fails silently on SQLite (thus inserting duplicate objects, breaking another test)

So I implemented a small helper that recursively serializes only arrays, making all tests pass.

[villasv]

villasv@PC  ~/projects/sequelize-fixtures   json-handling  npm test

> sequelize-fixtures@1.2.0 test /home/villasv/projects/sequelize-fixtures
> mocha tests

  fixture (with promises)
    ✓ should load fixture without id
    ✓ should load fixture with id
    ✓ should accept buildOptions in fixture
    ✓ should accept saveOptions in fixture
    ✓ should not duplicate fixtures
    ✓ should load multiple fixtures
    ✓ should not duplicate fixtures whose keys already exist
    ✓ should load fixtures from json
    ✓ should return model count and models
    ✓ should load fixtures from js (implied relative)
    ✓ should load fixtures from js (explicit relative)
    ✓ should load fixtures from js (absolute)
    ✓ should load fixtures from multiple files via glob
    ✓ should load fixtures from multiple files
    ✓ should load yaml fixtures
    ✓ should throw errors if files are missing
    ✓ should load assosication with. natural keys
    ✓ should load assosication with. ids
    ✓ should load many2many assocs by nat keys (41ms)
    ✓ should load belongs 2 many assocs by nat keys
    ✓ should load belongs 2 many assocs by ids
    ✓ empty many2many should not break
    ✓ should load many2many assocs by ids
    ✓ should set many2many even if object already exists
    ✓ should handle primary keys not named "id" for has many
    ✓ should handle primary keys not named "id" for belongs to
    ✓ if transaction specified, it should be passed to models
    ✓ if transaction specified, should load many2many assocs by nat keys
    ✓ should load fixtures and then transform their values
    ✓ should load user modified fixtures
    ✓ should add attributes to many2many through table
    ✓ should perform a set operation if one exists
    ✓ should add attributes to many2many through table using ids
    ✓ should exclude VIRTUAL columns from filter condition
    ✓ should handle json including arrays

  35 passing (2s)

[villasv]

I'm going to squash a single commit

[villasv]

Relates to #68 and #120

[villasv]

I'm still not sure this is going to work with PostgreSQL, but unless we somehow add it to the test suite, I guess the only way to fix this definitively is patching Sequelize itself.

[villasv]

Closing as stale, maybe some day this can be picked up.