Relative refs in parameters and schema are not resolved correctly

[mkistler]

If the value of a $ref is a relative reference but does not start with ".", the swagger core (specifically GenericRef) treats it as an internal ref. E.g.

"$ref" : "./path/to/model.json#/thing"

is treated as a relative URI but

"$ref": "path/to/model.json#/thing"

is treated as internal.

According to #306, this is intentional behavior in swagger core:

we added a convenience for a 1.2-style spec, where references did not need the full anchor.

So the parser needs to account for this by transforming actual relative refs into something that swagger-core will not try to treat as an internal ref.

The fix for #306 added code to make this transformation to relative refs that appear in properties. The same fix is needed for parameters and schema.