Allow searching by error

The full text search feature does not appear to work when searching by error message. For example, if I look at `/jobs/failed/1..1`:

```
[
{
"id":"2660941",
"type":"remove",
"data":{
"guid":""
},
"priority":0,
"progress":0,
"state":"failed",
"error":"No GUID specified for removal",
"created_at":"1410980651534",
"updated_at":"1410980651539",
"failed_at":"1410980651538",
"attempts":{
"made":1,
"remaining":0,
"max":1
}
}
]
```

If I wanted to find all failed jobs with the error message, "No GUID specified for removal", this is not possible today. `/job/search?q=No%20GUID%20specified%20for%20removal` results:

```
[]
```

Start at the `/job/search` entry point and compare its search behavior with the failed-job records returned by `/jobs/failed/1..1`, especially the `error` field. Done means a query for `No GUID specified for removal` returns matching failed jobs instead of an empty result.

Written by the indexing model from the issue text.