Replace core Search module with Apache Solr

[jim]

Issue & background
During work on #610, it was discovered that of a 1/4GB database dump for TN.org, ~80% (180Mb) of it was related to the Drupal 6 core Search module.

It's worth noting ​this was ​raised when we migrated the site to the Puffin server in March 2013, but it's generally the case that the core Search module does not scale easily beyond a few thousand nodes.

www.transitionnetwork.org has 23,803 nodes at time of writing -- this is probably approaching the sensible limit of the core module's capability.

Note also, any future D7 or D8 version of the site would also hugely benefit from using Solr, so the server config part is time well spent.

Proposed solution

1. Add the Apache Solr option to BOA, re-run the installer to get it installed and configured automatically.
2. Add the ​ApacheSolr module and any related required modules to the TN D6 makefile -- it's not clear if the 6.x-3.x branch or 6.x-1.x branch is the right choice at present.
3. Build a new platform containing these modules, migrate a clone of STG to it.
4. Enable the modules, configure them, disable core Search.
5. Create a feature that wraps up config for Solr and required modules. Add to Git, add reference to feature to makefile
6. Test, tweak, repeat 3 & 4 & 5 as needed.
7. Migrate PROD to the new plaform, enabled feature, index site.

This could be parked until D7/8 migration, or not... Ed's call.

[ed]

Well spotted Jim; thanks. Park it for now - all big jobs (like this) are on hold; main focus for you - knowledge transfer and handover to the others.