Fix binary/utf8 issues with Differential changeset parse cache

Summary:
Fixes T4898. After we increased the strictness of the `%s` conversion, most `serialize()` output is rejected from the cache.

Drop the cache, change the column type to latin1_bin, and then use `%B` to mark the data as binary during query construction.

Test Plan: Viewed Differential, saw cache fills.

Reviewers: btrahan, spicyj

Reviewed By: spicyj

Subscribers: epriestley

Maniphest Tasks: T4898

Differential Revision: https://secure.phabricator.com/D9171