When the key asked to index is a redirect, index the redirected location.
Fixed an error on /borrow page.

It was unable to handle /books/ia:xxx pages.
Added a script find works that are not indexed in solr.
Disabled deleting ia:xxx identifiers from solr on updating work.

The works in in_library subject were getting wiped off for unknown
reasons. I suspect that this might be a cause. Disabled temporarily.
Forgot to comment the code in the last commit.
When solr is stale, find the editions of work from database.

Shouldn't we be doing this always? Don't know why this was done this
way.
Optimized the find-indexed-works.py script to query Solr with 1000 keys at once.

This is way faster than the previous attempt.
Delete entries from Solr when a work is deleted.