Ignore node_modules directory. Fixes #4452

Fixes #4457.

docs/client/full-api/concepts.html

@@ -141,6 +141,13 @@ <h2 id="structuringyourapp">Structuring your application</h2>
     Any directory named `tests` is not loaded anywhere. Use this for any local
     test code.
 
+- **node_modules**
+
+    For compatibility with node.js tools used alongside Meteor, any directory named
+    `node_modules` is not loaded anywhere. node.js packages installed into
+    `node_modules` directories will not be available to your Meteor code. Use
+    `Npm.depends` in your package `package.js` file for that.
+
 ### Files outside special directories
 
 All JavaScript files outside special directories are loaded on both the client

tools/package-source.js

@@ -1241,6 +1241,10 @@ _.extend(PackageSource.prototype, {
                     //     suddenly start treating it as part of the main
                     //     app program.
                     /^programs\/$/,
+                    // node.js based tooling often uses dependencies which
+                    // are installed into node_modules in the root of the
+                    // project.
+                    /^node_modules\/$/,
                     /^public\/$/, /^private\/$/,
                     /^cordova-build-override\/$/,
                     otherUnibuildRegExp].concat(sourceExclude)