[mysql] surface unsigned numeric types

[Etomyutikos]

I'm not 100% sure what the equivalent is for Postgres, but the problem that prompted this issue doesn't exist there.

In MySQL, numeric columns can be unsigned. Unfortunately, the DATA_TYPE column does not report that (but the COLUMN_TYPE column does). It's impossible to have a uint or its variants in Go with the currently exposed data. It's therefore possible to send invalid values to MySQL (such as negatives).

[natefinch]

doh. yeah, gotta fix that.