Making the schema matching for case insensitivity more flexible.

The checks for text/string fields were incomplete when building case insensitive queries. In a few spots the schema checks were checking for a type = 'text', but were not checking for the other equivalent (given a pg backend) permutations.

For example, given the following set of attributes, only the fourth would be treated in a case insensitive manner for an equality check. The others would be treated in a case sensitive manner.

```javascript
    // 1
    firstName: {
      type: 'string',
      required: true
    },
    // 2
    lastName: 'string',
    // 3
    address: 'text',
    // 4
    address2: {
      type: 'text',
      required: true
    }
```
I found this while working through some of the failing sails-postgres integration tests