Fix type-specific keywords require a type definition in the schema

[bugventure]

According to the JSON-Schema spec:

When the primitive type of the instance cannot be validated by a given keyword, validation for this keyword and instance SHOULD succeed.

An important implication to this statement, is that any conforming validators must validate according to the defined type-specific keyword if the value type matches the type for which the keyword applies. request-validator fails to observe this requirement and does not apply type-specific validator functions, if the schema does not explicitly state the type of the value to validate.