Implementing TextMarshaler overrides my Schema

[uberbrodt]

Hi, I noticed that when I implement TextMarshaler on a type, the schema that I set through a Preparer interface is ignored. Looks like it gets picked up by isWellKnownType in reflect.go before PrepareJSONSchema is called.

I'd like some way similar to what was done here, #62 but to make sure it's type is not overridden because it implements TextMarshaler.

[vearutop]

You're right, TextMarshaler is a fair indicator to add type string, but it definitely should not prevent further processing.