Improve webpack custom build support for external node packages

[haydnhkim]

Use core-js custom build with webpack but, it doesn't work by path error.
I can show you a simple example.

step 1.

$ mkdir core-js-test && cd core-js-test

step 2.

$ npm install --save-dev webpack core-js

step 3. make test.js file

require('core-js/build')({
    modules: ['es5'],
    blacklist: ['es6.number.constructor'],
}, function(error, code) {
    if (error) {
      console.log('core-js build error');
      return;
    }
    console.log(code);
});

step 4. run test file

$ node test.js

you can see the console.log(code) in terminal.

/**
 * core-js 1.2.1
 * https://github.com/zloirock/core-js
 * License: http://rock.mit-license.org
 * © 2015 Denis Pushkarev
 */
!function(__e, __g, undefined){
'use strict';
/******/ (function(modules) { // webpackBootstrap
/******/    // The module cache
/******/    var installedModules = {};

/******/    // The require function
/******/    function __webpack_require__(moduleId) {

/******/        // Check if module is in cache
/******/        if(installedModules[moduleId])
/******/            return installedModules[moduleId].exports;

/******/        // Create a new module (and put it into the cache)
/******/        var module = installedModules[moduleId] = {
/******/            exports: {},
/******/            id: moduleId,
/******/            loaded: false
/******/        };

/******/        // Execute the module function
/******/        modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);

/******/        // Flag the module as loaded
/******/        module.loaded = true;

/******/        // Return the exports of the module
/******/        return module.exports;
/******/    }


/******/    // expose the modules object (__webpack_modules__)
/******/    __webpack_require__.m = modules;

/******/    // expose the module cache
/******/    __webpack_require__.c = installedModules;

/******/    // __webpack_public_path__
/******/    __webpack_require__.p = "";

/******/    // Load entry module and return exports
/******/    return __webpack_require__(0);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ function(module, exports, __webpack_require__) {

    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es5\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.object.freeze\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.object.seal\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.object.prevent-extensions\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.object.is-frozen\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.object.is-sealed\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.object.is-extensible\""); }());
    (function webpackMissingModule() { throw new Error("Cannot find module \"./modules/es6.string.trim\""); }());


/***/ }
/******/ ]);
// CommonJS export
if(typeof module != 'undefined' && module.exports)module.exports = __e;
// RequireJS export
else if(typeof define == 'function' && define.amd)define(function(){return __e});
// Export to global object
else __g.core = __e;
}(1, 1);

I fixed it just replace absolute path instead of relative path of core-js modules.
and it works fine both npm run grunt build and external node package build.

[zloirock]

Ok, thanks.