[PATCH] Improve Bitten database model

[Alexandru Chirila <chirila.s.alexandru@…>]

We have been experiencing problems with the current database model, specifically a very large bitten_report_item table (15 gigabytes). As a result: slow backup, slow queries on Build Status page, slower inserts etc...

A possible improvement to this is to split the table into smaller ones. The patch shards the table on the name field, which can only have these possible values:

('status', 'name', 'fixture', 'file', 'duration', 'type', 
 'description', 'lines', 'line_hits', 'percentage', 
 'category', 'msg', 'line', 'tag', 'traceback', 'stdout')

[Alexandru Chirila <chirila.s.alexandru@…>]

Patch that splits the bitten_report_item table.

[Alexandru Chirila <chirila.s.alexandru@…>]

Please note that the patch also updates the required tests, and also bumps the schema_version to 13 and provides a method to upgrade to the new version, by using trac-admin upgrade.

Tests are all passing.