improve Boolean validation and normalization

This corrects issues with the Boolean improvements introduced in 1.36. Existing Form Processor instances would not have been affected by these bugs unless they attempted to use the new features introduced in 1.36.

• I reverted the validateValue() changes in !37 (merged). Validation is, of course, on the raw values, and is unaffected by how this class returns the value from doAction().
• Testing showed that passing a lowercase y or t was not resolving to TRUE.