R1:31e1653a4e45

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…