In the HTTP cache for the API, the response_body field is marked as a

BLOB field and can contain arbitrary data. Previously when a cache entry

was updated, the content being inserted into the response_body field

was not being marked as binary, which caused issues when dealing with

diffs that had non-ASCII characters. This patch fixes that issue by

ensuring the the response body is being saved as binary when the field

is updated.
A unit test has been added to verify that non-ASCII data can be written

to the HTTP cache without error.

Ran unit tests.
Verified the supplied unit test fails without this patch applied.