Allow user to query by (multiple) collections

[Alex Cowell <al...@gmail.com>]

Hello,

We are a group of final year computer science students at UCL. We have been
assigned to work on SolrCloud as part of our group project.

We have started to work on the following unimplemented features as detailed
on the SolrCloud wiki:

- Optionally allow user to query by collection
- Optionally allow user to query by multiple collections (assume schemas are
compatible)

We have approached these problems by using the cloud state to retrieve the
slices for each specified collection, then adding them to a Map of all
slices to query, which in turn is mapped to the physical shards. We are
currently in the process of developing unit tests for our code.

We're open to feedback and we'll keep this list updated with our progress.

Alex Cowell, Soheb Mahmood, William Mayor, Konrad Kowalski, Ahillen
Kuganesan, Andy Gamblin, Hamza Sethi