Allow Route 53 to work with zones that have health checks.

I have tested the following scenarios:
* Weighted record with health check.
* Latency based record with health check.
* Failover based record (primary and secondary) with associated health check.
* The alias versions of all the above.
* Setting the "Evaluate Target Health" option for alias records.
* Printing out records with all the aforementioned setups. So "route53 get" works and gives you information about health records.

Some notes:
* "Evaluate Target Health" defaults to "false".
* "Failover Record Type" has no default.

Remaining items to do:
* Upgrade "zone.py".
* Write tests.
* Upgrade the route53 utility.
* Update Route 53 to allow it work with health checks directly.

The code I'm using to test the new features looks like this:

```python
import boto
from boto.route53.record import ResourceRecordSets

conn = boto.connect_route53()
changes = ResourceRecordSets(conn, "<example.com_zone_id>")
change = changes.add_change("CREATE", "test2.example.com", 'A',
    identifier = "alias-health", health_check_id = "<health_check_id>",
    failover_type = "SECONDARY", alias_evaluate_target_health = "true")
change.set_alias("<example.com_zone_id>", "test.example.com")
print changes.commit()
```

This would add an alias (test2.example.com) that checks the health of the target record and is itself a secondary record in a failover configuration. Printing the zone's records would, along with the usual information, give us:

    ALIAS <example.com_zone_id> test.example.com. Check alias health: true (Failover id=alias-health, Failover Type=SECONDARY, Health Check id=<health_check_id>)