title: Django haystack how is fq(solr) populated
body: <p>I am using solr as search backend with django-haystack. When viewing the logs I can see that query to solr is having "fq" populated. </p>
  
  <p><code>INFO: [] webapp=/solr path=/select/ params={fl=*+score&amp;start=0&amp;q=yyy&amp;wt=json&amp;fq=django_ab:(xxx)&amp;rows=10} hits=5 status=0 QTime=0</code></p>
  
  <p>My doubt is how this how is "fq" parameter i populated by haystack. I am using SearchQuerySet.filter to add search in solr documents.
  Another thing I noticed is no matter what the search query is fq remains same. Is fq related to the django application whose model is indexed? Should I be worrying about having it a constant.</p>