Convert `pushlog` and `refcursor` to BLOB storage

Summary:
Fixes T5840. Some time ago I incorrectly believed that `latin1_bin` collation was synonymous with "binary". It is not, and does not permit UTF8 characters outside of BMP, among other sequences.

These two tables currently have `LONGTEXT` columns which should be `LONGBLOB`. The table design is explicilty intended to accommodate invalid/unreasonably long ref names, but the collation prevents this from working properly.

After T1191, we'll have a general system for resolving this, but a user hit an issue yesterday (T5840) with a brnach name containing Chinese characters.

Test Plan:
  - Tried emoji inserts into both tables, was rebuffed.
  - Ran migration.
  - Performed emoji inserts into both tables.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5840

Differential Revision: https://secure.phabricator.com/D10217