Since WL#8020, we now leak MySQL-specific typedefs (uchar, my_bool, etc.)
into the client namespace when including mysql.h. This is bound to cause
problems for users sooner or later, and also reintroduces the dreaded my_bool
type. Get rid of them again.

Change-Id: Ie2358999558f61b1a501884388cd6ae7f07770d8