Prevent UnicodeDecodeErrors from being swallowed

UnicodeDecodeError is a subclass of ValueError, so these exceptions were being swallowed by the InvalidParameterError handling.
Update exception syntax
Add test to ensure UnicodeDecodeErrors not swallowed

This test registers a title indexer that forces a UnicodeException during the creation of an content item, and checks that it is not swallowed by api.content.create
Merge pull request #151 from plone/unicodeerror

Prevent UnicodeDecodeErrors from being swallowed