syncbase: Authorization helpers for recursively checking Resolve.
Added helpers for authorization with verifying Resolve on all
ancestors and returning fuzzy errors (ErrNoExistOrNoAccess) when
caller is not authorized for Exists(). Authorization now uses
explicitly listed tags, providing more flexibility than RPC method
attached tags (e.g. allowing multiple tags, checking different tags
on Database and Collection, etc.).
Updated Exists() RPCs to use the new authorization helpers.
Expanded tests to cover Exists() permission checking. More tests
will be added in subsequent CLs to cover error fuzzifying.
12 files changed