Normalization of HTTP-X headers should be optional

I'm working on a Google Storage API, and while doing that I discovered that all HTTP_X_GOOG_* headers are normalized to x-amz-* entries in the x_meta_map. This breaks the signature checking when authorizing because GS always sends the X-Goog-Api-Version header, which gets normalized to x-amz-api-version and hence become wrongly part of the canonical headers in the authorization signature.

Adding a boolean to the init_meta_info allows to override this default behaviour. It normalizes HTTP_X_GOOG_* header to x-goog-* entries in the x_meta_map.

Signed-off-by: Roald J. van Loon <roaldvanloon@gmail.com>