Possible issue in resolving recursive references #64
Description
I think I found an issue with the way references are resolved by the SchemaManager::fromUri() method.
If I use a call to SchemaManager::fromUri() to initialize the SchemaManager and then use that manager to validate a response whose schema involves recursive references, the validation goes off into an infinite loop.
However, if I use the SchemaStorage to import the json schema first (thereby pre-resolving all references) and then create the SchemaManager manually from the resolved schema, everything works fine.
Attached is a test case that I built starting from the example reported by @MaikWagner in #53 . Depending on which way the SchemaManager is instanciated (the test includes both ways, one comment and the other not), the test either is green or goes into an infinite loop.