Incremental saves, more resilient job queueing, impact index bug, deprecated redis server location

This release adds:

• Incremental updates using $set, $unset etc. for much more performance when saving to large CBDs (see #71)
• Deprecated MONGO_TRIPOD_RESQUE_SERVER in favour of RESQUE_SERVER. There can only ever be one resque server in your app.
• Better detection of redis fails, with 5 retries (see #79)
• Bug with impact indexes on views (see #76)