Resolved a test error with JRuby.
Resolved an issue with paging DynamoDB responses.

DynamoDB responses with attribute values failed to paginate as
expected, raising an error instead. The root cause was the
DynamoDB simple attribute plugin would modify the request
context params on the first request and then attempt to re-modify
the same params again on the next request made by the pageable
response.

As a fix, the response paging plugin now runs much earlier in the
stack. Before sending the request up the handler stack, it copies
the params into the context as `:original_params`. When sending
follow-up requests it always uses the original params. This isolates
it from changes made by other handlers in the stack (such as DDB
simple attributes).

Fixes #105
Removed 'Limit' from DynamoDB paging config for Scan.