Responsible for verifying the correctness of a legacy XML backup.
Currently this verifies that roles and groups within a directory have
different names (case-insensitive comparison).
NOTE: this class is stateful so do not use it in a singleton manner.
Verifies an XML document to ensure:
1. no group name matches any other group name in the same directory
2. no role name matches any other role name in the same directory
3. no group name matches any role name in the same directory
Errors can be obtained by called getErrors.