Fix persitent-mysql's handling of Unique for Text.
Fix persitent-mysql's handling of Unique for Text.

meteficha/persistent,meteficha/persistent,gbwey/persistent,andrewthad/persistent,superduper/persistent,pseudonom/persistent,gbwey/persistentold,jcristovao/persistent,nakaji-dayo/persistent,rdnetto/persistent,mitchellwrosen/persistent,gbwey/persistent,jcristovao/persistent,nakaji-dayo/persistent,mkscrg/persistent,mkscrg/persistent,mkscrg/persistent,jasonzoladz/persistent,gbwey/persistent,nakaji-dayo/persistent,rdnetto/persistent,mitchellwrosen/persistent,creichert/persistent,andrewthad/persistent,psibi/persistent,greydot/persistent,superduper/persistent,junjihashimoto/persistent,junjihashimoto/persistent,meteficha/persistent,superduper/persistent,gbwey/persistentold,bitemyapp/persistent,paul-rouse/persistent,naushadh/persistent,mitchellwrosen/persistent,pseudonom/persistent,jcristovao/persistent,greydot/persistent,erikd/persistent,andrewthad/persistent,jasonzoladz/persistent,greydot/persistent,jasonzoladz/persistent,plow-technologies/persistent,yesodweb/persistent