- remove need for defining "getTargets()" method as 95% of validators use same one
- replace abstract "Constraint::getTargets()" with one that use 95% of validators
- add additional tests for "Constraint::getTargets()" method
- remove unused "use" statement in Constraint\Valid
The constraint "Valid" does not accept any options or groups anymore. As per
JSR303 1.0 final, section 3.5.1 "Object graph validation" (page 39),
properties annotated with valid should be cascaded independent of the current
group (i.e. always). Thus the group "*" is not necessary anymore and was
removed from the "Valid" constraint in the Form validation.xml.