make default PKs for mysql unsigned by default

[MasterOdin]

closes #1780

This changes it so that the default PK for a table (either by not specifying one at all, or just setting the id option for the table) is unsigned by default, instead of signed. This gives users extra space to store IDs in their databases, and is generally considered the "right" definition to have for an auto incrementing column for mysql, with some amount of other ORM / DB stuff out there doing this as well.

The principle downside is that foreign key columns will have to be specified with "signed" => false now, but I think is balanced out by the upsides of doing this.

[othercorey]

The principle downside is that foreign key columns will have to be specified with "signed" => false now, but I think is balanced out by the upsides of doing this.

This seems like a significant change. Why don't users who want an unsigned range specify it instead of adding this dependency? The default INT range is very large.

[dereuromark]

Is there any downside of this?
This seems like the right way to approach this for most keys, if not explicitly configured otherwise.