Support require('foo') for `/foo/index.js`

[hthetiot]

Many node js library need to support this to run backend packages with mr.

APP_MAIN=data/main-data-coordinator.mjson node .

Examples:

var errors = require('lib/errors');

Error: Can't require module "lib/errors" via "lib/highLevelConsumer" because Cannot find module 'lib/errors'
    at getExports (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:594:29)
    at require (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:707:24)
    at Module.eval (file:///Users/hthetiot/projects/Kaazing/tmp/message/node_modules/kafka-node/lib/highLevelConsumer.js:8:14)
    at Module.module.factory (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/node.js:72:32)
    at Module.module.factory (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:1259:52)
    at getExports (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:632:38)
    at Module.require [as mappingRequire] (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:707:24)
    at getExports (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:610:31)
    at require (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:707:24)
    at Module.eval (file:///Users/hthetiot/projects/Kaazing/tmp/message/logic/service/kafka-service.js:5:25)
    at Module.module.factory (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/node.js:72:32)
    at Module.module.factory (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:1259:52)
    at getExports (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:632:38)
    at require (/Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:707:24)
    at /Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/node_modules/mr/require.js:716:28

Unhandled rejection Error: Error deserializing "root" when loading module "logic/service/kafka-service' from 'logic/service/kafka-service' cause: Can't require module "lib/assignment" via "lib/consumerGroup" because Cannot find module 'lib/assignment'
    at eval (file:///Users/hthetiot/projects/Kaazing/tmp/message/node_modulesv4/montage/core/serialization/deserializer/montage-reviver.js:483:27)

var dir = './lib/';
if (process.env.BUFFERMAKER_COVERAGE){
  dir = './lib-cov/';
}

module.exports = require(dir + 'BufferMaker');