Solr backend: run() kwargs are passed directly to search backend
Solr backend: run() kwargs are passed directly to search backend

This allows customization by subclasses and also fixes #888
by ensuring that the custom field list prepared by 
`ValuesQuerySet` and `ValuesListQuerySet` is actually used.
celerityweb/django-haystack,sgaist/django-haystack,kuanyui/django-haystack,ruimashita/django-haystack,blancltd/django-haystack,eventials/django-haystack,Stupeflix/django-haystack,cyanut/django-haystack,dionysio/django-haystack,streeter/django-haystack,django-searchstack/django-searchstack,kybi/django-haystack,elishowk/django-haystack,sgaist/django-haystack,jannon/django-haystack,barseghyanartur/django-haystack,comandrei/django-haystack,streeter/django-haystack,barseghyanartur/django-haystack,comandrei/django-haystack,django-searchstack/django-searchstack,cyanut/django-haystack,blancltd/django-haystack,fisle/django-haystack,jannon/django-haystack,kybi/django-haystack,vitalyvolkov/django-haystack,vitalyvolkov/django-haystack,kuanyui/django-haystack,speedplane/django-haystack,barseghyanartur/django-haystack,Stupeflix/django-haystack,comandrei/django-haystack,blancltd/django-haystack,antonyr/django-haystack,speedplane/django-haystack,kuanyui/django-haystack,django-searchstack/django-searchstack,jannon/django-haystack,eventials/django-haystack,askaliuk/django-haystack,elishowk/django-haystack,Stupeflix/django-haystack,eventials/django-haystack,cyanut/django-haystack,antonyr/django-haystack,zeehio/django-haystack,elishowk/django-haystack,fisle/django-haystack,speedplane/django-haystack,askaliuk/django-haystack,dionysio/django-haystack,vitalyvolkov/django-haystack,celerityweb/django-haystack,ruimashita/django-haystack,antonyr/django-haystack,zeehio/django-haystack,sgaist/django-haystack,dionysio/django-haystack,zeehio/django-haystack,ruimashita/django-haystack,fisle/django-haystack,celerityweb/django-haystack,askaliuk/django-haystack,streeter/django-haystack