fix: prevent obsolete typed-functions from hanging around

In other words, if name a depends on b and b is invalidated (because
  of added implementations), then a must be invalidated as well.

  Also adds a specific test (custom/piecemeal) that tests this.

complex/negate.mjs

@@ -1,4 +1,8 @@
-import './Complex.mjs'
+import {numComplex} from './Complex.mjs'
 export const negate = {
-   Complex: [['self'], ref => z => ({re: ref.self(z.re), im: ref.self(z.im)})]
+   /* need a "base case" to avoid infinite self-reference */
+   Complex: [['self'], ref => z => {
+      if (numComplex(z)) return {re: -z.re, im: -z.im}
+      return {re: ref.self(z.re), im: ref.self(z.im)}
+   }]
 }