fix Constraint::getErrors implementation

- remove presentation logic from implementation and dont filter returned errors by array_unique, business logic requires getErrors to return all existing errors, even if it contains duplicates
- make Validator::getErrors() return the same filtered result as before and apply array_unique when setting errors on Validator instance

Author: alexmmm

src/JsonSchema/Constraints/Constraint.php

@@ -82,7 +82,7 @@ public function addErrors(array $errors)
      */
     public function getErrors()
     {
-        return array_unique($this->errors, SORT_REGULAR);
+        return $this->errors;
     }
 
     /**

src/JsonSchema/Validator.php

@@ -40,6 +40,6 @@ public function check($value, $schema = null, $path = null, $i = null)
         $validator = new Schema($this->checkMode, $this->uriRetriever);
         $validator->check($value, $schema);
 
-        $this->addErrors($validator->getErrors());
+        $this->addErrors(array_unique($validator->getErrors(), SORT_REGULAR));
     }
 }