Confusing behaviour of equality operator.

[nsbgn]

As it is, the equality operator can hold that v == o is false but o == v is true, if o is a type operation and v is a variable that is bound to o. This is confusing.

[nsbgn]

We should probably rename unifiable to match and remove the custom equality operator to alleviate this.

[nsbgn]

The above was done in 96a948a.

[nsbgn]

Note also that __hash__, introduced in db95ab8, violates the principle that x == y implies hash(x) == hash(y), for the same reason. The main reason I haven't removed it yet is that is that equality is often used in testing. Should define an .assertMatch() instead of using .assertEqual().