Compatibility with old SQLite versions

Using: CentOS 6,Python 2.7

Config file:
directory: ~beet/music
library: ~beet/data/musiclibrary.blb
import:
move: no
copy: yes
write: yes

run: beet import

```
File "/usr/local/lib/python2.7/site-packages/beets/dbcore/db.py", line 562, in mutate
cursor = self.db._connection().execute(statement, subvals)
sqlite3.OperationalError: near "DEFAULT": syntax error
```