Fix problem with Model#validate not clearing the _validatorInProgress property.
Fix problem with Model#validate not clearing the _validatorInProgress property.

jkieboom/mayhem,SitePen/mayhem,jessevdk/mayhem,SitePen/mayhem,SitePen/mayhem,jkieboom/mayhem,SitePen/mayhem,QuinntyneBrown/mayhem,jessevdk/mayhem,QuinntyneBrown/mayhem,jessevdk/mayhem,jkieboom/mayhem,jessevdk/mayhem,jkieboom/mayhem,QuinntyneBrown/mayhem,QuinntyneBrown/mayhem