wadindex: issue #125; handle Error objects from ZipFile

- Don't add the ZipFile object to the IndexDB until after the ZipFile
  is successfully parsed and files were extracted from it
Error: rename 'content_block' attrib to 'raw_error'

- Added notes in the POD about the format of the 'type' attrib
[JSON|XML]Parser: calls to Error update 'raw_error' attrib
Roles/Database: clarify "missing 'sql' block" error message
ZipFile: close #125; return Error objects for zip errors

- Removed eval{} wraps around zip operations now that the custom error
  handler is in place
- Set the default for the 'members' attribute to an empty array