Test *real* ctor defaults.

Rather than those for testcase's '_makeOne'.
Add namespace to query ctor / clone.
Typos.
Pass namespace when fetching results.

Fixes #170.
Make '_get_protobuf_attribute_and_value' rigorous about bytes vs. text.
Make '_get_value_from_value_pb' rigorous about bytes vs. text.
Add notes to docstrings about 'text' vs. 'bytes' semantics.

Addresses #233.
Merge pull request #255 from tseaver/170-query_namespaces

Fix #170:  handle namespaces in queries
Merge pull request #263 from tseaver/233-support_blob_value

Address #233: support blob_value in protobuf
Drop munging of 's~' prefix onto keys.

Fixes #121.

Note:  may conflict with PR #257 and #258.
Merge pull request #259 from tseaver/121-drop_dataset_prefixes_in_keys

Fix #121:  Drop munging of 's~' prefix onto keys.