Update JdbcDatabaseSnapshot.java

Sybase should be:

```
SELECT i.name, i.status, t.name FROM sysobjects t INNER JOIN sysindexes i ON i.id = t.id
WHERE i.status = 2 AND t.type = 'U' AND t.name = 'FOOBAR'
```

The table `sysindexes` contains the indexes (duh), where the status field with a value of 2 indicates a unique index: http://infocenter.sybase.com/archive/index.jsp?topic=/com.sybase.help.ase_15.0.tables/html/tables/tables34.htm

The table `sysobjects` has one row for each table, the type *U* means user generated: http://infocenter.sybase.com/archive/index.jsp?topic=/com.sybase.help.ase_15.0.tables/html/tables/tables34.htm

So, given a table `foobar`, with a unique index for columns `baz` and `zot`, the following changeset can be generated:

```
<changeSet author="vetleino (generated)" id="1393274379538-7">
       <addUniqueConstraint columnNames="baz, zot" constraintName="UC_FOOBAR_BAZ_ZOT" deferrable="false" disabled="false" initiallyDeferred="false" tableName="invoice_cashing"/>
</changeSet>
```