Per-request authentication is ignored

[beingryu]

When initializing new request (especially for batch request) with Request#new, we can specify :authorization and :authenticated options.

However in APIClient#execute the authorization object is being overwritten as the APIClient's authorization because the options object is set to an empty Hash.

Usually we can walkaround this problem by specifying API call request to APIClient#execute instead of creating a Request, but for Batch it is not possible.

[sqrrrl]

Fixed for 0.7 (soon)