Resolves Issue GRAILS-10982 - findWhere and findAllWhere not accepting GString Keys

This fixes the findAllWhere and findWhere, An Issue existed where a call like this

```groovy
def property = "name"
TestEntity.findWhere("${property}":"David")
TestEntity.findAllWhere("${property}":"David")
//Exception Thrown Class Cast Exception
```

This is Resolved , tests were also added to tck project (FindWhereSpec) which provides a few tests for the findWhere method and findAllWhere method.