title: Vim Ctrlp not parsing Ag (silver search) --ignore option correctly
body: <p>When using <code>ag</code> on the command line, like so:</p>
  
  <p><code>$&gt; ag . --ignore="*node_modules/*/node_modules" -l --nocolor -f -U -g ""</code></p>
  
  <p>I am able to avoid searching through any node_modules directories more than one level deep in my node services, which is the desired behavior.</p>
  
  <p>However, when I use the following in my vimrc, the node_modules directories more than one level deep are not ignored:</p>
  
  <pre><code>" Use The Silver Searcher https://github.com/ggreer/the_silver_searcher
  if executable('ag')
    " Use Ag over Grep
    set grepprg=ag\ --nogroup\ --nocolor
  
    " Use ag in CtrlP for listing files. Lightning fast and respects .gitignore
    let g:ctrlp_user_command = 'ag %s --ignore="*node_modules/*/node_modules" -l --nocolor -f -U -g ""'
  endif
  </code></pre>
  
  <p>How can I set up <code>ag</code> and <code>ctrlp</code> to correctly ignore those directories?
  Not sure if I need to use a different syntax (like regex) or some other gotcha when transplanting to vimrc.</p>
  
  <p>The reason I'm not putting this in the wildignore is that node_modules are ignored in my .gitignore, so I'm using the <code>-U</code> option to ignore any vcs files (thereby allowing <code>ag</code> to search node_modules) -- but this option also seems to bypass the wildignore.</p>