Merge pull request #42 from larshesel/vp

Strengthen tests by checking the correct error code is returned
Get rid of redundant tests for create/replace series

And make sure they test what they're supposed to
Merge pull request #41 from gsalgado/vp

Get rid of redundant tests for create/replace series
Lowercased error messages, cleared up comments, shortened some lines.
No functional changes.
Merge pull request #43 from teknico/vp

Lowercased error messages, cleared up comments, shortened some lines.
Add test of decryptExtendedKey error paths