title: Syntastic going passive mode
body: <p>It's been quite some time that I'm facing this annoying problem with syntastic.</p>
  
  <p>When running gvim and performing a <code>SyntasticInfo c</code>, without opening anything, it returns me :</p>
  
  <pre><code>Syntastic version: 3.5.0-72
  Info for filetype: c
  Mode: active
  Filetype c is active
  Available checkers: clang_check gcc make
  Currently enabled checker: clang_check
  </code></pre>
  
  <p>But as soon as I open a <code>c</code> file and do a <code>SyntasticInfo</code> I get:</p>
  
  <pre><code>Syntastic version: 3.5.0-72
  Info for filetype: c
  Mode: active
  Passive filetype: c
  Filetype c is passive
  Available checkers: clang_check gcc make
  Currently enabled checker: clang_check
  </code></pre>
  
  <p>As a result nothing is checked.</p>
  
  <p>Here is what is in my vimrc :</p>
  
  <pre><code>let g:syntastic_check_on_open = 1
  let g:syntastic_c_checkers = ['clang_check']
  let g:syntastic_c_clang_post_args = ""
  let g:syntastic_mode_map={"mode":"active", "active_filetypes": [], "passive_filetypes": []}
  </code></pre>
  
  <p>[Edit]
  Having tried to put <code>'c'</code> for <code>active_filetypes</code>, it doesn't change anything. Though, what is really weird, is that the active checking is not triggered if I don't do a <code>:so ~/.vimrc</code> and every time I open gvim. It's as if this option wasn't taken into account by gvim. 
  [/Edit]</p>
  
  <p>Thank you in advance for any help</p>