title: Do not execute postinstall when installing package as dependency
body: <p>I have a package <code>x</code> that has postinstall script. During development I used it to do some tasks that are needed during development of this package.</p>
  
  <p>Now I've published this package. When installing it with <code>npm install</code> (<code>x</code> is listed as dependency in package.json) I don't want to execute postinstall task and this is not needed for package to be used as runtime dependency. </p>
  
  <p>Is is possible to achieve it?</p>