title: How do I unset a variable in Vim?
body: <p>I have a plugin that sets a global variable and checks it each time the plugin is loaded to avoid loading itself multiple times.  I would like to allow reloading of the plugin (allow reloading of the plugin) without altering the plugin itself.  The plugin simply checks to see that it's variable exists (i.e. <code>exists('g:var_name')</code>)—is there a way to unset said variable so that the <code>exists()</code> check returns false?</p>
  
  <p>p.s. I don't want to alter the plugin itself because I use <a href="http://vimcasts.org/episodes/synchronizing-plugins-with-git-submodules-and-pathogen/" rel="noreferrer">pathogen with git submodules</a> pointed at the plugin's repo.</p>