Feature request - fq and boost function for MLT

[Gagandeep singh <ga...@gmail.com>]

Hi solar folks

Looking at the current MLT implementation of solr, it gives good results
but there is no way of specifying boost function for it like we can for
search query. Currently at Bloomreach, we are using solr MLT for showing
products related to a given page and it works great, but we wanted to do
more with it like:

   1. Filter out results that are out of stock
   2. Give low boost to products which have 0 price
   3. Use geodistance filter in the MLT results - documents farther away
   from the main product should score lower

Considering these and more use cases in mind, i have generated a quick
patch which touches MoreLikeThisComponent and MoreLikeThisHelper to provide
this functionality with the following 2 params: *mlt.qf* and *mlt.multboost*
.

I would like to commit this patch if possible. What do you guys think?

Thanks
Gagan