default invalid_solr_id_error just a default 404 much like ActiveRecord::RecordNotFound

For #756
Merge pull request #766 from projectblacklight/simple_404_for_record_not_found

default invalid_solr_id_error just a default 404
No need to check for Turbolinks defined.

If there's no Turbolinks, we registered an event handler
for an event that will never be hired -- this should not harm
anything.

But the check introduces possible order-of-load errors, where
blacklight core accidentally ends up loaded before turbolinks,
so doesn't set up the event handler, but then turbolinks loads later,
so the event handler was needed, but didn't load. ran into this
with an engine that inserted it's 'require x.js' before turbolinks.
Best to avoid order-of-load dependencies if we can; we can.
Catalog#additional_response_formats should be a protected method as it's not routable
Merge pull request #769 from projectblacklight/skip_turbolinks_precheck

No need to check for Turbolinks defined.
Merge pull request #770 from projectblacklight/protect_addtl_respns

Catalog#additional_response_formats should be a protected method as it's...
Merge remote-tracking branch 'upstream/master'
Fixed indentation
Fixed tests to support bug fix #765