Classes with generic mixins applied to base do not parse correctly

[bennypowers]

consider

interface C {}
class B<T, U> {}

function F(s: any) { return class G<T, U> extends s {} }

export class A extends F(B)<D, E> implements C {}

export class _A extends B<D, E> implements C {}

Expected:

implements on line 6 parses as implements_clause

Actual:

implements on line 6 parses as part of a binary_expression in the extends_clause

See also atom/language-typescript#57