R1:d5bf30bb48ad

Prepare database for UTF-8

Summary: D1830#8

Test Plan:
`scripts/sql/upgrade_schema.php`
Try adding duplicate SSH Public Key - failed.
Try adding new SSH Public Key - succeeded.

Reviewers: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1852