vanilla/vanilla — pull request #2236 by imnotjames (2014-11-05 06:31:38+00:00)
Title: be explicit over nullable fields in GDN_MySQLStructure

Mark columns as explicitly null when they are marked as such in the structure

Per the MySQL column definition this is perfectly fine:

```
column_definition:
data_type [NOT NULL | NULL] [DEFAULT default_value]
[AUTO_INCREMENT] [UNIQUE [KEY] | [PRIMARY] KEY]
[COMMENT 'string']
[COLUMN_FORMAT {FIXED|DYNAMIC|DEFAULT}]
[STORAGE {DISK|MEMORY|DEFAULT}]
[reference_definition]
```