add resolveModuleSource option - closes #471

test/fixtures/transformation/api/resolve-module-source/actual.js

@@ -0,0 +1,3 @@
+export { foo } from "foo-export-named";
+import foo from "foo-import-default";
+import "foo-import-bare";

test/fixtures/transformation/api/resolve-module-source/expected.js

@@ -0,0 +1,5 @@
+"use strict";
+
+export { foo } from "resolved/foo-export-named";
+import foo from "resolved/foo-import-default";
+import "resolved/foo-import-bare";

test/fixtures/transformation/api/resolve-module-source/options.js

@@ -0,0 +1,5 @@
+exports.blacklist = ["es6.modules"];
+
+exports.resolveModuleSource = function (originalSource) {
+  return "resolved/" + originalSource;
+};