Relax Explode validator isValid value type, defer to bound validator
Merge branch 'hotfix/3530'

Close #3530
Fixes #3507
Merge branch 'fix/explode-validator' of git://github.com/cgmartin/zf2 into hotfix/3527
Merge branch 'hotfix/3527' into develop

Forward port #3527

Conflicts:
	library/Zend/Validator/Explode.php