Remove unique filter of where clauses

[matthewmcgarvey]

Fixes #487

With the addition of OR to the query builder, where clauses can no longer be uniquely filtered because two clauses are not equal just because they have they same condition, they could be separated by an OR and affect the outcome if removed. For example, these two clauses are not the same but the current query builder would turn the first into the second because of the way it checks for uniqueness:

SELECT *
FROM users
WHERE name = 'Paul'
    AND age = 18
    OR name = 'Paul'
    AND age = 100;

SELECT *
FROM users
WHERE name = 'Paul'
    AND age = 18
    OR age = 100;

This will not affect any queries negatively as truly duplicate conditions are handled as expected by Postgres.

[jwoertink]

This looks good. I wonder if we can come up with some sort of query analyzer deal at some point to help sort of bring this back in. Since one of the main goals of Avram is to help catch bugs in development, and part of that being poorly written SQL (i.e. slow queries, duplicate where clauses, etc...), it would be nice to figure out a way to add something to help catch things like this.

For now, I don't think there's much we can do, so this is probably ok.