git_caches#command_output using 'blob' not 'longblob' (truncates git cache silently)

Not actually sure how to fix this in a migration (seems to be an activerecord issue?) but I had to execute the SQL:

```
DELETE FROM git_caches;
ALTER TABLE git_caches CHANGE command_output command_output longblob;
```

in order to store (cache) git responses greater than 64K (irrespective of my mysql' max_allowed_packet size.
