Add Postgres all as builtin function

[spiffytech]

The all API is just like any's. Whereas any is used for 'is this value present', 'all' is often used for 'is this value not present'. Since they go hand-in-hand, it feels appropriate that since we have db.fn.any(), we also have db.fn.all().

[koskimas]

When is all useful? It just checks that the array (or other expression) is full of one single value?

[koskimas]

Oh, right. You can do "not in" using foo != ALL(array).

[spiffytech]

Yep: any and all are often used for semantically similar work to in and not in, but for working with arrays.