Merge branch 'release/1.5.1' into production
Merge tag 'v1.5.1'

1.5.1
validations: include more details in `err.message`

Modify ValidationError constructor to include the model name and
a human-readable representation of the validation errors (messages)
in the error message.

Before this change, the message was pointing the reader
to `err.details`.  Most frameworks (e.g. express, mocha) log only
`err.message` but not other error properties, thus the logs were
rather unhelpful.

Example of the new error message:

    The `User` instance is not valid. Details: `name` can't be blank.
Merge pull request #116 from strongloop/feature/improve-validation-error-toString

validations: include more details in `err.message`
1.5.2
Merge branch 'release/1.5.2' into production
Merge remote-tracking branch 'origin/production' into production