title: vim takes long time to scan tags when complete
body: <p>my vim will scanning tags for a long time when press tab to complete.
  I don't know it is about plugins or vimrc file.
  it really annoy.
  my vimrc is:<a href="https://gist.github.com/anonymous/5591546" rel="noreferrer">https://gist.github.com/anonymous/5591546</a></p>
  
  <p>it seems when I press tab it even scan the /usr/include directory,it take long time,it makes me crazy.</p>
  
  <p>such when I edit a file like:</p>
  
  <pre><code>#include&lt;stdio.h&gt;
  #include&lt;ioste&gt;
  main()
  {
      int x = 8;
      float y = 9.0;
      char z = 'a';
  
      int *p = &amp;x;
      float *q = &amp;y;
      char *r = &amp;z;
  
      printf("the *p address is %x\n",p);
  
      printf("%d\n", sizeof(p));
      printf("%d\n", sizeof(x));
      printf("%d\n", sizeof(y));
      printf("%d\n", sizeof(z));
      printf("%d\n", sizeof(r));
      printf("%d\n", sizeof(q));
      printf("%c\n", *r);
      printf("%f\n", *q);
  }
  </code></pre>
  
  <p>in include
  it will begin to tell scanning tags,and vim stuck.</p>